M3 OBDII vs. OBDI

I am posting for a friend who is looking for information on how to modify his 318IS. He is interested in doing a M3 swap and the 95 motor has OBDI and the 96-98 has OBDII. He has told me that there are complications using the OBDII motors. What are the problems and can they be corrected. The 95 M motor is harder to find and more expensive and thats why he wants to know if its worth it to try and find it or just go OBDII. Also does OBDII hinder performance modification at all. Thank you for your time.

PS: not interested in hearing about buying an M3 ... interested in the swap only