Try the Diesel Discussion forum.
On my OM603 which is pretty much the same engine as your OM602, there's a port towards the rear of the IP that lets you insert a lock which holds the pump to the housing. The lock engages when the crank pulley reads 15-degrees ATDC of #1. If the IP is off the engine, you'll have to pop the valve cover to be sure it's ATDC of #1.
If I understand the manual, you have to turn your engine to 15-degrees ATDC and install the IP with the lock in place. That should get you as close as you can without the mega bucks electronic timing tool.