Not model-engineering but; undying gratitude, and Beer tokens, available for a shunt-wound dynamo or DC motor along these lines: Preferably but not essential GEC, 500-750 watts, probably 50-70 volts at approx 7-10 amps. (110 volts would do). Mounting hole centres approx 4 1/4" front to back by 8" side to side. These dimensions suggest a short but large diameter dynamo from the early to mid 1920s and almost certainly without benefit of fan or interpole windings, though these details are not critical.
Thanks for any help