Kewl! I'm glad someone else has one of these...
conversions. I had planned to do a M30 turbo with a 635CSi I purchased, but the 745 turbo stuff that came with the car was junk. We elected to go for an LS1 (which is 100lbs lighter than the M30 it replaced)/T56 6-speed conversion. I've upgraded the software, but it's probably only putting out around 375 HP. It is also very sedate around town thanks to the massive torque.
My car's fast, but I would guess a E30 M3 with a LS6 transplant must be a screamer.