I am not an expert. I do know, however, that the 1985 model year vehicles have a few differences from the factory from the previous years. Also, in 1985 there are California market cars (will have a 722.4) and federal market cars (will have a 722.3 (SD would be 722.303)). See the chart below, and also this thread:
1985 diesel Mercedes upgrades - Mercedes-Benz Forum
1985 FEDERAL W/S/C123 (300D/TD/CD) = 722.315 transmission
1985 FEDERAL W126 (300SD) = 722.303 transmission
1985 CALIFORNIA W/S/C123 (300D/TD/CD) & W126 (300SD) = 722.416 transmission (300SD had a different tailcone for electronic speedometer - 100% interchangable with mechanical version)
I hope this is at least somewhat helpful, and that someone with more (and better!) information will chime in.
-Chris