Aristo Covered Hopper, Lowering & Kadee Installation

Aristo Covered hopper, Lowering & Kadee Coupler Installation
Ted Doskaris
October 31, 2009 Initial Release as Rev. GE-B

October 3, 2010 Rev. GE-C - Added material, including Appendix A & B

This vignette will describe a method for how an Aristo-Craft covered hopper car can be lowered and equipped with body mounted Kadee model 830 or 789 straight shank type coupler assemblies without modifying the car itself.

The Kadee 830 box is relatively large and includes a single longitudinal spring loaded coupler within it whilst the 789 box is smaller and includes a dual spring loaded coupler having a lateral affect. Both types have self centering coupler characteristics.

Lowering the car & Aligning its floor

For installing body mount couplers on the Aristo Covered Hopper car, there are two significant items that must be addressed first:

1) Lowering the car

As with many Aristo rolling stock products, this car sits too high from the rail head.
In order to lower the car, some folks have done surgical modifications of the car in order to lower it - namely, cutting out the car's bolsters and replacing them with modified or newly fabricated ones of a lesser height.

I have not done this as the car will remaining intact as it comes from the Aristo factory.

Accordingly, I chose to replace the original Aristo Bettendorf type truck assemblies with USAT brand Bettendorf trucks (USAT part no. 2033) - albeit modified as later illustrated in drawings.
These trucks are fairly inexpensive to purchase from USAT via Charles Ro Supply Company as they don't come with wheels. If lacking metal wheels, RLD Hobbies packages them in 4 axles to a bag for a reasonable price as shown below.

I modified these trucks by lowering their bolsters 0.220 inch - this value being about the practical maximum limit so as to retain their rigidity and pivot without interference when mounted on the car.

The unmodified USAT Bettendorf truck is shown at the left with the modified one at the right. The below picture shows the under side view. Note the coupler tang must be removed  to clear the axle.

The USAT trucks lend themselves well to the modification whilst preserving their rigidity - something impractical and virtually impossible to do with the original Aristo trucks.
Shown below is the overall resultant 0.300 inch distance from the top of the side frame and  bolster.

When these trucks are mounted on the covered hopper car, there is some minimal, non objectionable, lateral rocking allowed. This affords a desirable amount of articulation with car operation on less than perfect track work since USAT trucks do not include actual working springs as found in the originally installed Aristo trucks.

2) Aligning the car's floor with the end sill

The Aristo covered hopper car as new out of the box typically must have its floor popped into its intended position at the open end areas of the car. But once doing that, the floor's end area will typically not line up flush with the car's end sill as there is no mechanical connection by design.
Shown below is how the floor typically bulges downward below the car's end sill.

With the car supplied and operated with truck mount couplers this would not be an issue, but when using body mount couplers the floor must be aligned with a consistent attitude, ideally by having its underside surface being made flush with the end sill.

In order to align and secure the floor to the end sill, I made use of a small metal clip modified from what was originally intended as a terminal for an electrical crimp, but the clip can be newly fabricated as will be shown later in a drawing. The metal clip fastens to the floor and extends over the lip of the end sill.

Adapting some common item to use for the floor retaining clip like those shown installed in the cars of these pictures helps so you don't have to fabricate the entire clip from scratch.

I happen to have a box of terminals intended for mating with push-on electrical crimp type connectors. I was able to alter these terminals by using small needle nose pliers and other tools to make the required bends in the same locations like that of a completely fabricated clip as will be illustrated in a drawing. For the clip's fingers, I cut the end off near the outer edge of hole.
Shown in the foreground of the picture below are a couple of altered retaining clips, and in the background are a few terminals as they came out of the box.
Notice the dimple that is almost in the exact place where the hole is to be drilled and tapped for its no. 2-56 screw thread.

With the car lowered and the floor aligned, a spacer shim of about a tenth of an inch is also required to be placed between the Kadee coupler box and the underside of the car.
This spacer is virtually the same for both models of Kadee boxes. Its dimensions will be shown later in a drawing.
Shown below is the black plastic spacer resting on a Kadee 930 coupler box assembly ready to be mounted on a Union Pacific test car. Note that spacers and shim thickness values may somewhat vary from car to car depending on tolerances, including truck modification consistency. (The truck modifications will be discussed later and shown in a drawing.)

By design, the Aristo covered hopper car floor surface where the coupler box mounts is not completely level across its entirety. Use of the Kadee 880 gauge is of great value for checking the coupler alignment during the shimming and leveling process.
To level the Kadee 830 coupler assembly in the example Wabash car shown below, a thin washer of 0.032 inch thick is placed under the rear extremity of the box. Again, this value may vary somewhat. 

Similarly, to level the Kadee 789 coupler assembly as shown below, a rectangular shim of 0.010 inch thick (provided in the Kadee 789 kit) was slid under the tail end of the 789 box before the box was fastened down with a rear screw.

The test cars:

1) Wabash car

My first example car to try the Kadee installation on is the Aristo Wabash covered hopper.

Shown below is how dramatic this example car appears with an original Aristo truck left in place at the left and the modified USAT truck installed at the right.

Shown below is an underside view of the car having modified USAT trucks on both ends with an installed Kadee 830 box at the left and Kadee 789 box at the right . Note how the truck is allowed to pivot a bit more before its wheels touch the smaller 789 box. This may be of benefit for operation on curves tighter than 8 foot diameter - which is what these cars easily work on with the 830 type boxes.

2) Union Pacific car

I decided to do a second car to check for consistency. In this case I installed the model Kadee 930 at both ends of the car.

The Kadee 930 assembly is the same as the Kadee 830 but made in a brown color, thereby better matching cars painted with brown or "box car red" colors.
Since these model Kadees have relatively large boxes, I believe color matching cars exhibiting open end type structures tends to lessen the more noticeable visual impact of the larger size box. In this regard, a more prototypical look would favor using the smaller model Kadee 789 box.

Installation considerations & tips

1) Coupler box Mounting screws

Only two screws are used to mount either the Kadee 830 or 789 coupler boxes utilizing the in-line holes of the boxes, and the screws are 0.75 inch long no. 2-56 as supplied by Kadee with the 830 boxes.

If using the 789 box, you must drill a hole centered through this box nub recess area for its forward mounting screw to pass through it. As shown the example below, a washer placed within the nub recess can be used to help center the drill.

The forward mounting screw for each box also serves as the fastening screw for the floor retaining clip. The rear screw's length must be trimmed so it does not protrude much past the floor for the end of the car having the brake assembly - otherwise it will interfere with it, whereas, the forward screw need not be trimmed as there is a hollow recess in the assembly that envelopes the longer screw. For the end of the car devoid of the brake assembly, the screws' lengths can be trimmed for best aesthetics.
The brake assembly of the car is held in place by 3 small self threading screws from the underside of the car. Two screws retain the brake valve and air tank.

The forward most screw head at the brake valve will interfere with the shim used under the coupler box on this end of the car so the shim is to be notched as shown in the drawing to follow. Alternatively, this screw could be removed (left out); however, when installing the forward coupler box screw, you need to press your finger on the forward end of the brake assembly so the screw won't push up on it. Since this portion of the brake assembly is offset from the center line of the car, the screw will have a desired effect of digging into one side of it within its hollowed area, thereby helping to retain it.

2) Shims

The shim material I used for the coupler box spacer included a plastic strip purchased in bulk at an inexpensive price from Tap Plastics. For example, I had them cut a 3/32 inch thick, 3 foot long by one inch wide black colored strip. I sliced off what was needed with a razor saw to the dimensions of that shown in the drawing to follow. I chose the 1 inch dimension since this best fits within the flat portion of the floor pad area when placed lengthwise.

3) Threading floor holes

The purpose of using a tap to make threads in the car floor and metal floor retaining clip is to save one the difficulty of trying to place small 2-56 nuts within the interior confines of the car - particularly on the end having the brake assembly so it would not have to be unfastened; but if you wish, you can body drill for the 2-56 size holes and use the nuts that are supplied by Kadee. Alternatively, self threading screws could be used or used in combination with previously described methods.
Consequently, for the example test cars, I did not have to remove the brake assembly.

4) Floor retaining clip alternative - only when using Kadee 789 box

As an alternative to the metal floor retaining clip (applicable only when using the model Kadee 789 coupler assembly) the hole that is provided to secure the 789 box lid with small screw could be somewhat enlarged to accept a long screw to pass through the box such that it could thread into the car's end sill lip - thereby serving to fasten the coupler box lid whilst at the same time securing the floor flush with the end sill of the car. However, the upper side of the lip (as shown below with clip) will be at risk of becoming aesthetically compromised if the screw were to break through its center rib.

If you are willing to do so, you could trim off the center rib and take advantage of a center flat area of the lip to install the screw from the top down - passing through the 789 box to secure it.

Dimensional Drawings

The following includes drawings that illustrate where to drill holes in the car floor for mounting either Kadee 830 or Kadee 789 type coupler boxes, the required floor retaining clip, and the modifications required of the USAT Bettendorf trucks:

Kadee 830 or 789 coupler box mounting Locations, etc. - Specific details

The Kadee 830 type box uses hole locations 1 &  3 as shown in the drawing.

As shown below, the car's floor holes for mounting the coupler box can be located and marked with a scratchall tool by pricking the soft plastic. The resultant dimple will facilitate drilling the holes.

I use a pin vise to drill out the floor holes to the desired size as indicated in the drawing.
Typically, I start with a small pilot drill, then progress to the finished drill size.

A pin vise with the finished drill size is shown below. Also, note the notch at the tail end of the black shim on the coupler box is to clear the floor screw that retains forward section of the car's brake assembly.

The holes are then tapped for the Kadee supplied no. 2-56 screws as shown below.

As shown below, the Kadee 789 box has a different rear screw location than the 830 type box. Either box type only requires two screws, but the rear screw is located differently.
The Kadee 789 box uses hole locations 1 & 2 as shown in the drawing. 

Lowering the USAT Bettendorf truck - Specific details

The new in the bag USAT Bettendorf truck assembly must first be disassembled by removing the screw that secures each side frame to the truck bolster ends, after which the side frames can be withdrawn. The side frames are made with pockets that accept the truck bolster ends.

As can be seen in the above drawing, lowering the USAT Bettendorf truck requires 4 modifications that involves: (1) removing 0.220 inch from the height of the side frames' pocket, (2) removing the same value 0.220 inch from ends of the truck bolster sides, (3) notching out a small section of the rib on the underside of the truck bolster, and (4) removing the bolster's coupler tang.
The following detail description is expressed mostly in terms what material is to remain on the side frames and truck bolster rather than what is to be cut off:

1) Cutting down the USAT Bettendorf truck side fame pockets

The USAT truck appears to made of a nylon type material - it being somewhat though to cut, but using a fine tooth razor saw works well.

Shown below, the razor saw is used to make the lateral depth cut of the side frame's pocket.
The scale is helpful to initially locate the saw. Though in the example depicted here the scale appears to be at about 0.200 inch, move the scale as needed to make sure the desired amount of the pocket that is to remain is to be 0.235 inch as per the drawing.  

Shown below is how the saw has penetrated through the pocket wall of the side frame.

Shown below, the razor saw is being used to make the slice parallel with the side frame - stopping when reaching to the desired depth.

Shown below is the USAT Bettendorf truck side fame with completed cuts made to its pocket.
Note, If mistakenly taking off too much material, you can use small piece/s of duct tape acting like shims to build back up the pocket height. If taking off too little, you can file down the pocket to the desired height.

Any cleanup of the side frame pocket cuts is done with a file as shown below.

When done, the desired result is to have the side frame pocket height measuring 0.235 inch. As shown below it's a bit short by 0.010 inch - correctable by using a small piece of duct tape placed on the lip of the pocket to build it back up.

Shown below is how the cut down pocket of the side frame on the left compares with the original on the right.

2) Cutting down the USAT Bettendorf truck bolster sides

Shown below is one of the sides of the truck bolster. Both sides are to be cut so that 0.335 inch remains. (As depicted in the upper part of the picture, the distance from the upper side of razor saw to the top of the bolster.)

When done, the desired result is to have the height of the sides of the truck bolster measuring 0.335 inch as shown below.


In the event either the side frame pocket or bolster side were cut a bit too short, it is to be appreciated that the longer of the two will dictate the overall assembled result of the truck. For example, if the side frame pocket were to be less than its targeted 0.235 inch height but the bolster side height is at its targeted 0.335 height, the assembled truck will be OK. Likewise, if the bolster side height were to be less than its targeted 0.335 inch height but the side frame is at its targeted 0.235 inch height, the assembled truck will be OK.
This, of course, may not work out if either of them were grossly wrong. 

3) Notching the underside of the truck bolster

Notching is required so that the bolster sides are allowed to seat all the way into the side frame pockets when the truck is reassembled.

A small rib section next to the side of the truck bolster must be cleanly removed down to base surface. Using a razor saw to do this is shown below to make the initial cut at a distance of 0.070 inch, minimum.

You can use a small needle nose pliers to bust off the small piece after the cut is made and clean up with an X-acto knife and small file held on its side as it passes through the cut out area of the rib.

4) Remove the coupler tang from the truck bolster

Due to the lowering, the axle will interfere with the coupler tang when the truck is reassembled, so the tang must be removed far enough inboard of the axle.

Reassemble the modified truck with wheels and check results

Install the wheels between the side frames and the bolster into the side frames' pockets.
Use the original screws to secure the side frames into the bolster. A properly modified and reassembled truck will feel rigid and strong just like the unmodified truck when attempting to wiggle the side frames.

Checking the result after reassembly should yield a measured distance of 0.300 inch on both sides of the truck as shown below. If one side is different than the other the car can assume a lopsided stance. If much less than the 0.300 inch value, the car will sit needlessly high requiring more shim distance between coupler boxes and body of the car. If much more than 0.300 inch, the truck won't fully seat over the pivot post of the car body bolster as the side frames with rub against it when the truck pivots. Adding a spacer washer over the truck bolster pivot post may mitigate this.

Accordingly, if not 0.300 inch, corrections must be made. Take the truck apart. First try swapping the side frames at the bolster ends and recheck for the proper 0.300 inch measurement on both sides.
To correct, if more than 0.300 inch is measured, you can use small piece/s of duct tape acting like shims to build back up the side frame pocket height and / or truck bolster side ends. If less than 0.300 inch, you can file down the height of the side frame pocket and / or the bolster side ends to the desired height.

Car Coupler Alignment Results:

Shown below is the Aristo Wabash test car with the model Kadee 789 installed as coupled to the Kadee 880 gauge.

Shown below is the Aristo Union Pacific test car with the model Kadee 930 installed as coupled to the Kadee 880 gauge.

As shown in the above pictures, it is to be appreciated how the floor retainer clip's fingers straddle over the car's end sill lip. This serves to align the floor with the end sill whilst keeping the end sill from pushing out due to forces incurred when its retaining screw is tightened down.

The Weight of the Completed Car:

Shown below is an example Frisco Covered Hopper car with lowered USAT trucks having USAT metal wheels that measures 2.31 lbs.

Comparing the finished car:

Shown below is the end view of an Aristo UP covered hopper car as factory equipped with Aristo trucks but with ART-29111B metal wheels retrofitted. Having no mechanical retention by design, note how much the floor bulges downward by what appears to be its entire thickness!

For comparison, shown below is the like kind car with the modified (lowered) USAT trucks and Kadee 930 body mount coupler installed (Note the dramatic space difference between the side frames and body bolster between the two cars. Ditto for the wheel to floor proximity.)

Though it looks like the side frame of the modified USAT truck is touching the body bolster, the truck pivots OK. Also, note how well the floor is flush with the end sill in the center area where the coupler box is located. The floor retaining clip is responsible for accomplishing this.

Shown below is a side view comparison of two Aristo Union Pacific covered hopper cars. The car on the right has the lowered USAT trucks and body mount Kadee couplers whilst the car on the left is "factory" but for its metal wheels.

Note how the hopper dump areas of the lower car is closer the rail head - it being in line with the lower ends of the truck's journal boxes. When examining pictures in books of prototype covered hopper cars, this appears to be very prototypical.

Shown below is an end view of the UP car with lowered USAT trucks and body mount Kadee 930 couplers installed so the car's overall height can be appreciated.

Shown below are GP40s & SD45 pulling a 45 car test train with the Aristo Wabash and UP covered hopper test cars.

Car operation on 10 foot diameter track

The USAT SD70 is one of the worst case locos that can be used for testing operation of a car on curve tracks with respect to coupler action and any possible tendency to force a car off the tracks. This is because of the long wheel base of the loco along with its unfavorable as designed truck pivot location - the two of which combine to project this loco's front pilot (and coupler) to an extreme outer position on curves. 
My USAT SD70 is custom fit with body mount swinging Kadee 787 medium offset coupler box assemblies. (The swinging box helps mitigate the ill effects of the SD70 design.)

Shown below is an overhead view of the SD70 coupled to the Wabash covered hopper test car with the Kadee 789 body mount assembly on a 10 foot diameter track curve.

Shown below is an overhead view of the SD70  coupled to the other end of the Wabash test car with the Kadee 830 body mount assembly on a 10 foot diameter track curve.

Both coupler box types performed well with the SD70s pulling a 45 car train.
However, the vertical displacement of the SD70 coupler on the curve section of the track was better when coupled to car having the Kadee 830 assembly.
Since the SD70 has medium offset Kadee 787 couplers, there is a natural tendency for them to tilt downward when loaded with a heavy train. So such characteristics are not unexpected.

In this regard, when I did the same test with Aristo GP40s or SD45, there was virtually no vertical coupler displacement. The GP40s and SD45 I used are equipped with custom fit body mount Kadee 789 center set couplers.
Shown below is an overhead view of a GP40 coupled to the Wabash test car with its body mount Kadee 789 in a 45 car train on a 10 foot diameter curve track.

Shown below is an overhead view of a GP40 coupled to the UP test car with its body mount Kadee 930 in a 45 car train on a 10 foot diameter curve track.

Car operation on 8 foot diameter track

I also tried testing the car on 8 foot diameter curve track. My layout is mostly 10 foot minimum diameter worst case for its main line, but rail yard access uses 8 foot diameter track - so I could not test a long heavy train load on this area of the layout.
That said, the Aristo Wabash test car with Kadee 830 on one end had no problem when the car was artificially loaded with my hand at one end with the SD70s coupled to the car at the other end.
Shown below is an overhead view of my SD70 having modified swinging Kadee 787 box coupled to the Wabash test car with Kadee 830 on an 8 foot diameter curve.

However, when I turned the car around and coupled the end having the Kadee 789 box to the SD70, the car - when artificially loaded - would tend to left its front truck inside wheels from the rail head.
Shown below is an overhead view of my SD70 having modified swinging Kadee 787 box coupled to the Wabash test car with Kadee 789 on an 8 foot diameter curve.

The below picture shows the side view of the Wabash car with Kadee 789 coupler when coupled to the SD70. The wheels are lifted above the rail head when artificially loaded in this circumstance. This did NOT happen when trying the car with an SD45.

Irrespective of what is a prototypical mismatch, it is not expected to use an SD70 to pull such cars on tight curves as 8 foot diameter, but if done it appears the Kadee 830 on the Aristo covered hopper car is the better choice here. The Wabash test car with the Kadee 789 operated OK without incident on the 10 foot diameter curves with the USAT SD70 and long train, and the car was also OK when coupled to either of Aristo's SD45 or GP40 on 8 foot diameter curves - which would be more of a prototypical lash up - given such cars were likely long gone when the SD70 entered service on the real railroads.
That said, the overall results of installing either the Kadee 830 / 930 or 789 type coupler assemblies in conjunction with lowering the car solely owing to truck modifications and using a floor retaining clip worked beautifully.

Appendix A - Installation Techniques for the Coupler Box & Floor Retaining Clip:

The example car used here is the Aristo Rock Island covered hopper - shown with its installed, modified USAT lowered trucks with USAT wheel sets and the newer Kadee 906 couplers. The traditional Kadee 830 / 930 coupler assemblies work the same way. (Notice I took the opportunity to pre-paint both coupler box and floor retaining clip so they would be less noticeable.)

The reason for using a floor retaining clip can be seen as illustrated below.

Note how the floor bulges below the ends of the car. The reason for this is that the car is made with its four floor mounting posts recessed about 0.070 inch too much below the edge of the car whilst the end bulkheads are about flush with that same edge - thus, forcing the floor bolsters and ends upward as illustrated by angle of the rods.

The floor mounting screws could be backed out some to help minimize the effect, or the floor could be removed in order to put spacer washers on the mounting posts; however, doing so will further lower the bunker outlets - maybe too close to the rail head after the lowered USAT trucks are installed.

Another possibility is to trim off the bottom straight edge of the slide-in end bulkheads by about 0.070 inch, but then the floor would have to be allowed to recess further up into the car end areas. This would be a way to lower the car even more than described in this article and would require a less thick and dimensionally different coupler box spacer and retaining clip - a lot more work, and you would likely have to use some touch up paint, too.

As the car comes from the factory, occasionally one or both end bulkheads are not completely seated, and this should be checked before proceeding.

Now for the installation process:

The first thing to do is to loosely mount the coupler box with its spacer using both front and rear mounting screws.
Loosely mounting the box at both its front and rear holes keeps these parts from swinging around at the most inopportune time during the installation process.

A washer should be slid under the rear of the Kadee 830 type box.
I use a small no. 4 nylon washer. (Depending on cumulative tolerances, the washer thickness required for final leveling the box can vary anywhere from 0.030 inch to 0.060 inch.) At this point in the installation process, just use any thickness within this range.

Whilst aligning the coupler box with its spacer squared up over the floor, thread the rear screw in for a minimal snug fit.

Thread the front screw in so that its end just begins to appear above the plastic surface of the floor.

Now insert the floor retaining clip by angling it so that it will go under the brake valve

Assure the clip is centered once it is under the brake valve. It's OK if the clip assumes a  downward tilt when first inserted as it will tend to straighten out and align during the fastened process.

With the car placed upright and overhanging a bit on a table, hold on to the clip with your finger, then thread in the front screw.  It's OK if the clip lifts a bit off the floor whilst doing this as it will be cinched up later.

The screw is to be started into the floor clip that was previously tapped for a 2-56 thread.
Note: In the event the screw is unwilling to thread into the clip, the tip of the screw can be ground with a conical point for better locating itself into the clip's hole. I only had to grind a conical tip on the screw for 2 of 25 cars completed.

Before grinding the screw's tip, first put a couple of nuts on it so they can be subsequently backed-off for cleaning up the threads.

Once the screw is started into the floor clip the car can be turned on its side for torquing down the screw.

Since the plastic floor had been previously tapped to accept the screw for easing the  installation process, it can now be "stripped-out" as the screw is further tightened down completely. (As the metal clip accepts the force of the screw it will prevail over plastic.)

After all is done the coupler box should be snuged-up against the floor as shown below.  The nylon washer at the rear of the box can been seen, too.

Note the floor does not bulge downward where the coupler box is located.

Shown below is a black Frisco covered hopper car that had to have its coupler box front mounting screw ground with a conical tip to facilitate fastening the clip.

The lowered USAT trucks can now be installed as shown below on the Rock Island car.

With the car placed on a track, check for coupler leveling. I used the Kadee 880 gauge.  Note the coupler used in the example Rock Island car is the new Kadee 906, but the gauge is equipped with the Kadee 830. With this arrangement I looked to see that the couplers' horizontal casting seams lined up. If the couplers don't line up, check to see if the rear screw has a snug fit and use a different thickness rear washer as required. (Note, since the washer is against the sloped floor area, sometimes you can do leveling by just pushing it toward the end of the car or the center of the car - remembering to re-tightening the screw.)

The completed car is shown below at the brake wheel end with Kadee gauge.

Shown below is a factory Rock Island covered hopper car on the left and the lowered Rock Island car on the right.

Shown below is the factory car. It measures about 5.75 inches above the rail head to the top of the roof walk.

Shown below is the lowered car. It measured about 5.50 inches above the rail head.
So the car was lowered close to a quarter of an inch.

USAT brand metal wheels intended for use in their Bettendorf trucks are about 0.040 inch smaller in tread diameter as compared to Aristo's ART-29111 type metal wheels.

Using the USAT wheels as I did, therefore, contributed to half that amount (0.020 inch) toward lowering the car that when combined with the modifications made to a USAT truck resulted in an overall lowering of about a quarter inch (0.25 inch).  That quarter inch lowering amount may not seem like much, but as can be seen in the pictures it is profoundly better (virtually prototypical) whilst at the same time accommodates the Kadee coupler installation.

Appendix B - Lowered USAT Truck Having Tang Mounted Couplers:

For using the lowered Aristo Covered Hopper as transition car, its lowered USAT trucks can accept a tang mount Aristo (or Kadee) knuckle coupler - albeit with a weakened tang.

Instead of completely cutting off the tang to clear the front axle as previously described when body mounting couplers, the underside of the tang can be rounded out to clear the axle shaft.

To a minimize the amount of material removed, use of the USAT brand wheels is preferred in this application since its axle shaft is smaller in diameter than Aristo's ART-29111 axle.
As illustrated below, the USAT lowered truck with Aristo ART-29111B wheels (I painted them black) is out of level (slightly taller) than the USAT lowered truck on the right with its USAT metal wheels.

A round rat tail file can be used to remove material from truck tang.


When the truck parts are assembled and the axle is installed, ensure it turns freely when the truck is place on a track and rolled. Otherwise more material must be removed.

For mounting an Aristo Knuckle coupler to the USAT truck tang, I used a coupler assembly salvaged from an Aristo GP40. Note the nub end of the tang must be removed. If a bit too much of the tang's nub is removed, a spacer can be glued at the butt end of the coupler housing - as I did with the green pad as shown below.

I improvised a bushing made from the plastic part of an electrical crimp to fill in the GP40 coupler hole in order to mount it.
Shown below on the left side is the USAT lowered truck with Aristo GP40 knuckle coupler mounted, and shown on the right side is an Aristo Bettendorf truck assembly coupled to it.

For mounting a Kadee 789 center set coupler assembly - albeit with coupler installed upside down - to the USAT truck tang I fabricated a shim as shown below:

Note the nub end of the tang must be removed. Also, an extra hole was drilled near the tip of the coupler tang.

As shown below, a Kadee supplied shim can be tucked under the coupler assembly for leveling purposes.

As shown below, the lowered USAT truck assembly mounted and shimmed Kadee 789 coupler aligns with the Kadee 880 coupler height gauge.

Shown below is a comparison with the lowered USAT truck at the top with a Kadee 789, at the middle with the Aristo GP40 coupler, and at the bottom is the Aristo truck assembly with its Aristo knuckle coupler.