Replacing a crank shaft questions

ch1ll said

I believe they went to cast crank mid year 72 after they depleted inventory of forged cranks. I have a 72 with undersize crank from the factory.

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help me understand ch1ll, can one use an undersized crank if it was not “undersized” originally? The real question is; will your crank work in any 68-71 340? Or am I looking for a “Maltese Cross and an X” on my block for it to match?