The FSM (factory service manual) has all this information. The manuals are out of print but you can find them on eBay sometimes (at insane prices), or buy the CD-ROM from the dealership, or buy copies of the CD-ROM on eBay. The W124 manual is posted online and it includes the OM603 engine manual, which is what you need for your 300SDL.
Click here and check out Group 07 for the injection timing info.
The link to the procedure is below, note that it shows the use of the "A-B light box", which makes the job a breeze. This tool is expensive (~$300) and I'm not sure if anyone rents it. You can do the same job with the lock tool, however extreme care must be exercised, if you forget to remove the lock before rotating the engine, you can damage the IP. But, the lock tool is only $25-$30 or so (
click here). Only buy the
OE/dealer tool, not the aftermarket ones. There isn't any factory procedure showing how to use the lock tool to set timing but you may be able to find that somewhere on this forum:
http://www.w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/Engine/602_603/07.1-8240.pdf
Timing specs (basically, A-B or lock tool with crank at 15° ATDC) :
http://www.w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/Engine/602_603/07.1-1100.pdf
