people have been known to fit the v12's into e30's. there are a fair few m30b28 powered e30's getting around. you've just got to move a few things around the engine bay like the brake booster and the radiator overflow tank. just little things like that.
Ive done a little bit of research on E30 bmws, i think as m3s werent available in south africa, bmw m-sport (i think it was) conceived a E30 with a 2.8L from the 5 series. Wouldve gone like stink....