I have a 318, and dropped it, putting a z3 rack in next week and going to follow this guide to liven up the m42.
I contemplated a swap several times, but decided to keep it light weight in the end, and just take driving lessons. These cars are made to be driven by someone who knows how to drive it around the track. That's when you see the true potential of what a slow 4cyl lightweight 318is can do.
Car looks super clean though. I wish my paint looked like that still! I might suggest US or Euro ellipsoids. I can actually see at night now!