Many people over at the e30.de website has done this conversion. There was a E30 with a 7 series engine in it too. The 3.5l is big but im sure it will fit in the E30 engine dock. I wouldn't use the E30 Tranny, perhaps upgrade to a E36 Tranny or perhaps a 5 Series Tranny. I don't know anything about block numbers. I suggest you check out either e30.de and post on the message board or talk with people over at bmwe30.net. Sounds like a good project though. :)