i am sure that the age of this post has outlived the original asked question but future viewers may benefit
heres a post i started on big coupe with pictures and some info http://bigcoupe.com/phpBB2/viewtopic.php?t=5331 i am running a m30b35 and 5 speed from a 90 e34 in my 3/81 e12 based 633, i connected the motronic 1.3 to the 81s body harness and it actually wasn't all that hard, i chopped the fusebox plug off the l-jet harness and spliced it onto the plug from the e34 and passed the computer plug through the firewall and mounted the computer in the stock location above the glovebox, the fuel pump and main relays plug the main engine power are at the right side of the blower under the cover. i converted the rear suspension to the later e28 style with a 3.73 limited slip diff, to install a e28 rear suspension you need to add about 200 mm to the parking brake cable housings (the tubes that are attached to the body) and do a little plumbing to connect the brake lines, you need a early center mount diff cover from something like a 533 to connect to the stock e12 body mount

• 1978 630 CS mods...help needed - jarni2 2007-03-13 03:58:58 (372 views)
  • Re: 1978 630 CS mods...help needed - winfred 2007-10-19 23:53:47 (88 views)
  • Frame are different so diff wont swap. Engine & trans are doable if - bmw635 2007-03-13 12:31:46 (283 views)
    • Re: Frame are different so diff wont swap. Engine & trans are doable if - jarni2 2007-03-14 02:23:13 (299 views)
      • E12 chasis has different front cross member/ suspension mount - bmw635 2007-03-14 13:43:37 (314 views)
        • Re: E12 chasis has different front cross member/ suspension mount - jarni2 2007-03-14 16:21:47 (254 views)
        • Re: E12 chasis has different front cross member/ suspension mount - jarni2 2007-03-14 16:21:37 (312 views)
          • What country are you in? What's availab;e in your country so I can tell you the - bmw635 2007-03-14 16:36:11 (294 views)
            • Re: What country are you in? What's availab;e in your country so I can tell you the - jarni2 2007-03-19 16:45:23 (290 views)
              • M90 engine is 1977-81 ( 93.5mm bore x 84mm stroke), it's the same bottom end in - bmw635 2007-03-19 18:29:50 (339 views)
                • Re: M90 engine is 1977-81 ( 93.5mm bore x 84mm stroke), it's the same bottom end in - jarni2 2007-03-21 02:34:14 (328 views)
                  • Motronic engine will fit in L-jet car with 1 mod: feed power to DME since the (url) - bmw635 2007-03-21 13:02:30 (310 views)
                • BTW, the E12 exhaust manifold have to be used in newer engine since the exhaust - bmw635 2007-03-19 18:35:53 (275 views)