1966 slant six 170 timing mark

No. That's just where the balancer was balanced at the factory. The mark on the balancer is a small ding hash mark on the outside edge of the pulley grooves.
Thanks man. I'll clean that thing off and see what I can find. I was looking for a timing mark/slit in the top of the balancer but couldn't find it to save my life. Should there be a bolt in it going into the crank? I didn't feel one.