The mc kit with "ring grooves" is for a tandem mc, a snap ring goes in the groove to prevent piston over-travel. If the tach is mechanical type it would have a cable drive off the side of the distributor to rear of tach. But I think that year was a 12v tach? if so then it picks-up current from the neg. side of coil i beleive a white wire w/black tracer. hopfully i helped