I would imagine that if you are buying this as a dedicated track car, you have experience with this sort of thing.
I have heard that the stock weight balance can be retained by relocating the battery to the rear and installing a carbon fiber hood. If you get some nice wide wheels with sticky tires you should be able to put the power down nicely. Is the engine stock? Also, an LSD from an E30 would definitely help out in this situation.
There are a couple threads in the track forum where guys are running swapped tis. Check out some of those, I think you should definitely go for it.
http://www.318ti.org/forum/showthread.php?t=22179