Hi 5115 and sakuragi,
Thanks for the input. I think before as what you think, M50B25 more power advantage than M52B25, and both sharing the same torque specification, but M52B25's power and torque happen at the lower rpm compare to M50B25, which I assume that it will have a better power band and torque curve, plus save a little bit patrol. Considering the weight of the M52 engine almost the same with M20 range, it will have better weight distribution compare to M50 engine. The less power of M52 engine is due to tighter emmision control with tigher air intake manifold, can be swap with the M50 air intake manifold with minor modification, and I believe it will gain more power.
Need to learn more about the security system or EWS on the M52 engine. If possible, use back all the electronics stuff into E30 (centre console with digital air-con individual control will be "cool"). Is it possible?