The engine is supported between the gearbox and the engine bar hence the adaptor plate , you can get away with a Camper engine, universal case or bug engine with adaptor otherwise they pretty much the same 1600 TP, but you have the 72 so you could go for the T4 lump, which for a 72 strictly would be a 1700 pancake motor.
I take it theres nowt in the back at all then?