The only way to be sure is to use the positive stop I described and actually check for TDC. In 60-something years of building high performance engines, I've never managed to develop a thumb, screwdriver, or other half-donkey method of finding top center that's accurate enough to believe in.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!