I've done a few conversions myself, the latest being a 342" Ford and 5 spd in a 190. For conversion info on a Chevy small block into a 123 chassis go to www.JagsThatRun.com. They have books for each model for swaps into Z cars, Volvos, Astros, Jags and Mercedes along with hints, sources etc. Their main book, 11th edition, is available form the site or Summit Racing.
Good luck,
Tobias MB
4 MBs