Mercruiser 3.7 timing issues

[Trap Jaw]

So lets start from the beginning. We have been having nothing but problems with this motor since day one. Replaced just about everything with the ignition and fuel. Finally starting to run halfway decent. We decided to install an electronic ignition to rule out problems with the points(even though they're new). Started 10 times better after installation, but it backfires now and then. Talked to a few motor heads at work and they said that the timing would have to be advanced with the new ignition. So now to the problem.

Started the motor and warmed it up and hooked the timing light up. It wasn't till then that I realized there were no marks on the flywheel(ok not really the flywheel). So does anyone have any idea how I should go about timing this thing.