Am I correct in assuming those with a 616 and 617 indicate their respective engines? I should think Mercedes has at least some level of method to the madness.

I believe it indicates what engine the part first appeared on. In some cases, the part number gets superseded with a number for a later engine if the updated part is backwards compatible. For example, the injector end plug for the OM61x engines now has a 605 prefix since the updated part appeared on the OM605 engine, and the updated oil fill cap for some OM61x engines has a 111 part number because it first appeared on the M111 engine.

__________________
'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.

Got it. Thanks for the comeback

And that goes for more than the engines. Chassis parts follow the same architecture.

Re: OM616.912
I need an
A. intermediate gear shaft 'set'(2 pcs)
B. timing device bearing bushing
C. Thrust piece
The problem is that every online parts refernce Ive found lists THREE part numbers for each. Note: These part numbers were all specifically to 616.912 by reference to the parts diagam for the group. i.e. the same schematics in the black catalog that should be in the glove box of most w123s. I may be wrong but I dont believe these parts interchange with 617.912.
I.
A. 615 050 05 06
B. 615 052 01 06
C. 615 180 01 44

II.
A. 617 050 07 06
B. 617 052 01 06
C. 617 180 00 44

III.
A. 130 050 03 06
B. 621 052 01 06
C. 126 180 00 44


I know there are at least 2 if not 3 updated versions for each part as per the FSM but that doesnt help. Some but not all or compatible ut again the FSM is no help because they refer to version vs. part number. Complicating matters further is that I have a Mercedes factory rebuilt engine. M-B actually grinds off all of the engine number but the engine type '616' then they rivet a metal stamp to the block and assign a completely differnt number unrelated to the original. Ive no idea how to order most engine parts because I dont know the number.