could find the ('73) sheet in my manual for the factory setting but you wont go wrong w 10 deg before (w vac adv unhooked/plugged) and could prob go 12 or 15. If it doesn't labor when cranking and does not ping on accel on your hottest/driest day you are in good shape. Know that '73 was the worst year for emission controls to meet Fed smog standards and Ma used alot of mismatched systems to try to get compliance and you can make alot of gain w the driveability if you play w timing/mixture/cam timing if no smog testing in your area
