I have wasted literally billions of electrons trying to give people advice, which they promptly ignore. Once anything in a stovebolt ignition system gets modified, the wrench jockey is on his own regarding setting the timing, and there are plenty of self-appointed gurus who will be happy to give you reams of advice that doesn't make good nonsense. Different years and engine sizes have widely varying flywheel markings, and using the above "positive stop" method of establishing TDC is step number one. Any attempt to skip that step means you're shooting in the dark. My email is in my profile. If you'd like to have a discussion of ignition timing off the main forum, please email or PM me and I'll share a phone number. A 2-way conversation can accomplish more in a few minutes than a couple of dozen written messages can. That's why I spent 30-something years in a classroom, putting the next generation of auto mechanics out there.
The advice you've gotten about initial timing is a good example of insufficient, or downright incorrect information. If you use an initial timing of 20 degrees before top dead center, keep a fire extinguisher handy for the inevitable backfire and carburetor fire. 5-8 degrees of initial advance is much more appropriate.
Jerry
