Considering building up a e30 to a lightweight racecar is my dream project, just no time or money to do it properly, but if I was going to try, I would first off replace control arms, suspension system I advise Koni, brembo break with rotors and callipers, and first of all make sure your frame isnt rusted. Once you have good rolling shell, then I would try to reduce weight, after that, drop in stock engine with transmission, just not over 80k miles, and preferably M engine high rev, as in s62 or s54,(yes hard but worth it). and last is modify that endinge with software, intakes, turbo(in this case, since car is light) and maybe even bore it.
BEST OF LUCK! POST PICS SOMETIMES!