BTW, for those of you who haven't seen my "Engines" post on the M-B board...
Assuming the description's accurate (and I think it is, based on the pictures of the engine), that's an OM617.950. There were 3 variants of the turbo 5 cylinder available, and the .950 is the rarest of the three, as it was only used in '78 to '80 300SD's (the other two were used in '81-'85 300SD's and '81-'85 300D's respectively). The big thing about the .950 is that it's the only turbo OM617 design that doesn't have an EGR valve.
EGR valves + diesels =
I want that truck