cast crank converter question

OLDSTYLE said

It's possible to external balance the front and internal balance the rear. Look for heavy metal or welding done to the rear of the crankshaft.

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Yup, this is correct. My 73 340 is a externally balanced crank and balancer, but has internally balanced flywheel and clucth. The machine shop balanced it this way for me.
I can just never switch any of it, because it was all balanced together.It also runs smooth.