Well, there was no combines on the trains: an RPO, at least one baggage-express car, vestibule coaches and the obs car.
I believe that part of the power plant was in a box on the platform of the baggage-express car.
Back a 100 years ago some of the standard-gauge, mainline railroads put small steam driven dynamos in baggage cars to provide lighting power for the passenger trains.
Brian Norden