Im not 100% sure of everything that you will need, but a new diff and propeller shaft comes to mind.
The M3 Tranny will have different ratios on the gearing so these will have to be changed so the car dosnt go out of wack.
I would also hazard a guess that you may need different mounts. Im pretty sure they just done 'bolt out, bolt in'.
I will make a few more enquiries and make another post.