+1 for ^
I just did it recently because my flywheel slipped the key. Lapping is probably required for those flywheels and losing that key should be mandatory. I got the timing where I want it and filed a little alignment mark on the end of the shaft.
Also, I didn’t have (or want to buy) lapping compound. So I just rubbed a little Emory cloth against itself over a piece of paper. Mixed the grit with grease.