Jay, I have never seen an OM601 engine and have no clue. The OM603-961 IP has a plug near the aft part of the IP, when its removed, the cam fly weight area of the cam can be seen.

There is a lug that looks like the end of a straight screwdriver that the the cam lock slips over and holds while the IP is being installed. If the crank is properly set and the lock is in place, timing should be very close.

The go/no go gauge you asked about was a different situation. With the side plate removed, I discovered three of the control linkages disconnected. (these are my names for this stuff).

To reposition the runners into the slots with out undue force, it was necessary to loosen and slide the slot brackets down the rail and back. All I did was fashion a guage out of thick plastic (actually a battery tote strap) to fit between the brackets, right and left of the one I was moving. This allowed me to return it to the spot on the rail that it left.

Sorry I cannot provide more help.

Harry
86 300 SDL