The HARS C121C ( military eqiv of an L1049G) manual refers to a gas turbine APU. Our manual is a generic C121C and C121G manual. Our aircraft APU was removed during its storage in Pima and we have not been able to find a replacement so far.
The manual says that on the C121C, the APU can be used inflight in an emergency.The rating is 500amps. The unit was fitted in the rear of the fuselage. The controll panel is at the top of the FEs panel and certainly looks like it was fitted at the time of manufacture in 1955.It would be hard to understand why a blank panel area is there if an APU was not planned during construction.
We also have a Catalina which was originally fitted witha single cylinder petrol APU. The generator is at one end of the crankshaft and a bilge pump at the other. It seems to have been fitted in the area below the flight engineer's station, lwr left hand side with both exhaust and bilge water into the L/H wheel well area ( for those that had wheels).
Wunwing