http://www.034motorsport.com/product_info.php?products_id=665

Adapter plate for VR6 to Audi inline transmissions.

Obviously, they're AWD, but it's pretty close, just cap the front shafts, Bob's your uncle. Maybe drop the compression and slap some turbos on, or even find one of them fancy new 3.6L, from the cars not the minivan. Plenty of room, the VR6 is tiny compared to the Mercedes engines.