timing questions for '68 318

Either you

do not have the cam properly aligned (one tooth off)

or the balancer outer ring has slipped

or the balancer / timing tab are not matched, IE early to late

or a massive factory defect means that something was manufactured incorrectly

It is VERY difficult to "find" TDC by FIRST using the cam marks, as you have a certain amount of "dwell time" there

What is much easier is either use a piston stop to locate TDC or to first PUT the engine on TDC using the timing marks, them remove the cover and THEN look at the cam and verify it is correct/ not