hello
i put a 2.5di into my series 3 SWB to replace a two and a quarter standard unit.
it is not noisier than the old engine, is much quicker, and i can get over 35 mpg on a long run.
you do need a MILNER adaptor plate. you do need to remove part of the OS engine mount on the chassis and weld a bit in.
a couple of tiny cuts have to be done on the footwells.
You may need to provide an electric fuel pump. for some reason my bulkhead fouled the mechanical lift pump on the footwell.
Read Diesel BOB website on his opinion of the engine.
Plus.. no electrics other than oil switch, temp gauge and stop solenoid. it is very simple.
the land rover 200tdi is probably better, but costs lots more..