The prototypes were different lengths, with the FA-2 about two feet longer. That would account for the difference.
Mike
The shell from my Walthers FA -- which dates back at least 15 years, and which I believe is derived from the Train Miniature model -- will not fit over the Bachmann FA2 chassis. The Bachmann chassis is too long. So even if you remove the clear plastic strips on the internal side walls of the Walthers shell -- which serve as both the side door porthole glass and as tabs to hold the body to the chassis, in order to provide some clearance along the sides, that does nothing for the length problem. If you put the two shells side by side and align them at the windshield, the Bachmann shell has a visibly longer nose at the front, and visibly longer body at the rear, hence the longer Bachmann chassis. Bottom line -- you cannot get the Walthers shell on the Bachmann chassis, at least not without more modification than would be worthwhile.
I cannot speak to the MTH fit as I have not acquired any of the MTH units.
Does anyone know if the Walthers TL Alco FA body will fit with little or no modification on the Bachmann FA2 chassis or the MTH FA1 chassis?