Tony: It may very well be your 45 class, or an ancestor of it. Alco built a lot of export units that looked like RS-1s, 2s, or 3s, but with the low cab.
All I did to my units was lower the cab on an Atlas/Kato RS-3 shell and put it on a MT Z SD40-2 chassis. The truck centers are almost perfect, and the wheelbase is very close to the 4-axle RS-3, but it would be nice to have an Nn3 version of the RSD truck to fit the Atlas chassis. The shells are packed with lead sheet and putty, so they'll actually out-pull the original model.