Well, I don't know about doing a R107 SL, but at least it was designed for a V-8 engine. This conversion has been done in the past with these cars, at least with a 6.9 engine which is of similar size. I believe the owner of the MB dealership in Sacramento CA did this many years ago.

Over at M-100.org, we have a guy in Florida, Derek Jettmar, who stuffed a 6.3 motor into a R113 280SL. You can see the project at:

http://www.ritzsite.net/280SL63/01_SL63.htm

Cheers,
Gerry