Update on my research. It appears there was a LSD mid sized case R129 diff with 3.69's. It came in the early 300SL's that were automatic. (the manuals had 3.45's)

I happen to have one listed right now down by me here in LA.http://www.ebay.com/itm/MERCEDES-BEN...-/301410277612


This is a very interesting and informative read. I educated me on the backlash of an MB diff- impossible to do without MB special tooling because the backlash needs to be set up outside the case then re-measured for a blind fitment inside the case. Forget what I said about R&Ding a few case for parts swap on my own- not like a GM or Ford housing...lol. Damn Germans over engineer everything.
http://www.peachparts.com/shopforum/...tml#post513955