What engine do you want to put in it? Ive seen everything dropped into a E30: S52, S54, M5 V8, V10, even a twin turbo V12.
It's more about what your budget is and how much work you wanna put in. An M50 is an almost direct bolt in. Anything else will require custom fabrication work. You would be better off to just turbo the engine you already have in there.