Vacuum on 1968 GTS 340 4 spd.

OH yeah and once this is figured out get a new harmonic damper on there pronto, from here on out the outer ring will just keep slipping which is no bueno. You'll keep chasing timing marks that move and the crankshaft might eventually get damaged.
Good point... not to mention that if the ring has slipped and the rubber is cracked between the outer ring and hub, then the damper is no longer doing its job of the damping the internal high frequency crank vibrations. BTW, if you want to keep the old one, it can be rebuilt at a place like Damper Doctor; there may be other rebuilders too.