That's another issue entirely... easier just not to open that can of worms as the debate is old and fierce in certain circles.
All I will say on that subject is there was only 1 true M8 ever built by Motorsport themselves and it lives in the BMW Museum in Munich. It was powered by the S70/1 (550hp) - not the McLaren F1's S70/2 or S70/3. The 1,510 E31 850CSi's were powered by the S70B56 (375hp), a related but different motor. It would be like saying the M54 and S54 are basically the same... nope.
The prototype M8: