Thats what the simple dash mounted ignition power interupt toggle switch is for.
Easy hot starting. Be sure the GM OEM start motor brace is installed.
Why don;t you mark your balancer for 36deg BTDC (1/10th the circumfrence ) and 24deg BTDC (1/15th the circumfrence) of the balancer , from true TDC.
Find true TDC using a piston stop. I bet the timing tab location is out of wack.