The few vaguely similar cars that ATSF had were all GSC castings- some listed as built by GSC, and others as built by ATSF- I guess depending on which shop put the trucks under them and installed brakes.
What does the car length scale out to? That would help to ID the prototype, if any.
I used to think many of the Roco cars of various types had no prototype, but... I've found a lot of "very close" over the years, so I suspect most do have prototypes, its just that the details on the cars are often oversized, or they cheated a little here and there- door types, number of ribs in car ends, that sort of thing- to keep tooling costs down.
