Another thing it could be that a lot of people don't think of is the balancer has spun inside the hub. If it is still the original look to see if any rubber is sticking out. We had a mustang that would ping if you tried to set the timing at 12, When you would set it by ear and then check it with the light it would read something like 50 deg ATBC. Just trying to give you something else to think about.