383 Harmonic balancer question

Pippen said

Just noticed the flex plate is indexed meaning it only bolts on one way. I wonder why that is if it’s neutral balanced?

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The balance internal or external is not achieved with the flex plate. Just the converter or flywheel and balancer. That appears to be a steel crank, but if you can turn a rod throw straight up so we can see the parting line, we can confirm it.