The nicest conversion I ever came across was an MGB with the Daimler 2.5 V8 fitted. Lighter than than the original B series boat anchor, smooth and fast. I recall that the exhaust was a problem, but Mike the Pipe built one which fitted. Did not need any alterations to the suspension unlike the Rover 3.5. Don't know how available these engines are, though.
If BrileyMoCo or whoever they were at that time had their act together this could have been the MGD - they had all the bits in their parts bin.
GMacK