Dumb Timing question?
Have you timed it previously? Just for giggles, I'd buy/ get/ make a piston stop and check the accuracy of the mark. Here's the one I made IN THE SEVENTIES for my then 340. The dimension is not critical. Mine is not really adjustable. If you buy an adjustable one, examine it carefully. Many are wobbly without a locknut. You may had to buy a special nut with reduced hex size. You can get them at "real" fasteners shops
Have you timed it previously? Just for giggles, I'd buy/ get/ make a piston stop and check the accuracy of the mark. Here's the one I made IN THE SEVENTIES for my then 340. The dimension is not critical. Mine is not really adjustable. If you buy an adjustable one, examine it carefully. Many are wobbly without a locknut. You may had to buy a special nut with reduced hex size. You can get them at "real" fasteners shops