You wouldn't happen to have the VINs from the original vehicles? If so, you might be able to check the part numbers in the EPC.
I'm not sure I can isolate where the differences are (between various head revisions), but, with a comparison between the 300SDL and the 350SDL, the injector 'nozzle holders' have separate part numbers.
For the 126.125 (603.961 US) the part # is A0020172821
For the 126.135 (603.970 US) the part # is A0020174021 (replaced by A0030172921)
Having a #14 head, I'm inherently curious about differences between configurations (perhaps it's a defense mechanism built into my brain?). I just wish I could provide more useful information, but I haven't found much on the topic
