Thanks for all of the replies.

To my knowledge, all components (Crank, Harmonic Balancer, Flex plate and connecting rods) are stock and unmodified.

The harmonic balancer is a 6-pack balancer with 4 very small holes drilled in one side about 1/4" in diameter and less than 1/16 or 1/8 in depth. This could just be factory balancing, I'm not sure.

The 6-pack harmonic balancer came from the same engine as the steel crank and the 6-pack rods (from a 1970 block). The hyper-t pistons are new and were not drilled or modified. Not sure about the flex plate.

Thanks ~