There are several good reasons to fit a Rover engine to a Stag:
Size and shape. It is the same physical size as the Stag engine and fits perfectly in the engine bay which was designed for an almost identical engine.
Weight. Weight corrupts power and balance. The Rover engine is 100lbs lighter which has benefits all round, ie. performance (less dead weight to accelerate and brake) and handling. (See my article on modified Stags)
Reliability. You can have a lot more power if you want it and reliability.
Performance. The Rover V8 can be tuned to give huge increases in power reliably. A standard 3500 can be modified to give 200bhp quite cheaply and the Range Rover EFI (Electronic Fuel Injection) engines 300bhp, or even a good deal more depending on how much you are prepared to spend.
I can supply everything you need to do the conversion to a Rover 3.5, 3.9, 4.2 or even the 4.6 EFI (which is the engine used by TVR!). We will also offer free advice, help you find a suitable good 2nd hand engine, or even put you in touch with the right people (if needed) to do the rebuild including all the electronics.