Hi Christiaan, yes THAT was the MEPU (Good photo of G-BBDG by the way). As far as fitting an APU in the tail cone, I still personally think that UNLESS you are prepared to pass a sizable pneumatic duct
through a fuel tank, (Remember that tank 11 occupied the entire rear fuselage between the rear cargo aft wall and the front of the tail cone). then I don't think that this was really on. (It's quite possible of course that I'm missing something here, it comes with age
).
As far as the MEPU goes, all it really did was drive 2 hydraulic pumps; the Green System then powering the 40 KVA emergency generator; unless you are going to use the APU for engine starting and ground air conditioning, then I honestly don't think that there would be much point. It's interesting also to note that the MPU, being a rocket motor, needed no air intake, and as it was not driving any huge loads, the exhaust duct dould be quite narrow.
