You could fake it if you were so inclined, but the differences are fairly numerous.
The trucks were different, the fuel tank was shorter on the SDP40F, the rear generator portion was distinctly different, and there were countless little differences in grills, doors, etc. They were buit on the same frame, so if you're a stickler for the details you could maybe convince someone like Mark4Designs to create a resin shell to be interchangeable with the Athearn body.
EDIT: A quick search actually popped up a post on Trainboard by Robbman about someone actually making shell for these. Being Robbman, maybe Mark4Designs actually is looking into this...