More of a thump than a ring...
Lets try not to be too judgemental. He who is without wear, throw the first rod.
Anyhoo, synthetic oil is a bad idea for old motors. And when we say old, we mean wear-wise. I wouldn't switch any high-mileage motor to synthetic, because of the chances of increased leaking and oil pressure differances due to engine wear.
Just use Castrol 30W and change it when it turns dark brown, or 1,500 miles, whichever is first.
The less you disturb an old Chevy 6, the better. Once you change things, or go into one, there is no turning back, young skywalker!
good luck
chip
