The harmonic balancer is 9 1/4" diameter. I just used masking tape and made a mark for top dead center. Then I figured where I should be shooting and made a mark there. I also made a mark for stock setting in a different color. Then I ran the engine and found where it was set, made a mark and ran it again to verify. Then measured how far I needed to go and did it.
I have a full set of instructions I wrote with a tool list if you are interested.