1985 was an odd year for US-spec Diesels in that they had different transmissions. I'm not sure if that means different gear ratios only or won't interchange as well. Might have been an odd year for Euro Diesels as well. Further confusing because an 85 Euro can also be a W124.

I'd cross my fingers and go with something out of an 85 300Dt or TDt. If Nitske's accurate, the ratios are only off in the second decimal in first gear.

Sixto
95 S420
87 300SDL