need help a couple small block ????'s

ok ive heard of a couple people running magnum heads on their non magnum engines, but didnt really think much of it. well i just remembered that i have a set of magnum heads layin in the shop, but was wondering what the benifits or drawbacks were, or if they will even work? also i was wondering if someone knew could tell me any specks from the casting numbers? it looks like 5300, 6300, and 6671 on both? maybe the pictures will help. any information or advise will help thanks alot!!

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