Update

Checked top dead center by valve position method as well as #1 cylinder mechanical stop method and it appears on my 261 that TDC seems to be the circle on the flywheel ( not a bb or ball). Before the circle is a line that is approx 5-6btdc. On a previous post that showed a few varities of timing marks mine looks like the last one


Old Truck addict
1950 chevy 1 ton napco
1956 gmc 1 ton dually napco
1954 chevy 3/4 ton napco
1957 gmc civil defense napco panel