I've not seen a modified rear end, that actually gives you a multi-link rear end.
You may want to call these guys.. This is the best solution for a high horsepower car with the E30/Ti/Z3/m-coupe rear end.. But just makes it stronger, still uses trailing arms.
For the m-coupes, this is what the owners were doing when the trunk floor tears. The Ti floor and diff mount is a bit different, so I don't think their existing kit would work without modifications. But going to a dual ear diff cover is probably the best way to handle all the extra power.
http://forums.bimmerforums.com/forum...php?p=13136896 Randy Forbes
SPORTS CARS PLUS, LLC 419-350-1098
Randy is a member on bimmerforums.