Aristo FA VersionsThe two pictures below are courtesy of George SchreyerThere are 5 versions of the FA, and 3 of the FB.1st version in "silver-blue / gray" box, 2 lash screws on the motor blocks, holes in back of wheels, like a hubcap pressed in the back of the wheel.2nd version in black box versions, 2 lash screws, need to validate wheel type, believe holes gone3rd version had motor block with no lash screws, ball bearing wheels4th version (FA only) added the Aristo socket and changed to the new "prime mover" smoke unit.5th version (FA only) included a lowered floor, see Ted's vignetteThe FB unit never got upgraded past 3rd version.At some point, both locos were lowered... I believe it was about the time of the 4th version. Picture of "blue box" motor block Picture of "black box" motor block