Rear differential from 67 or 75 new yorker

What rear diff would be in a '67 new yorker with a 440 and what would be in a '75 New Yorker with a 440? I am looking for a rear that will handle 600 hp and I can get my hands on either of these cars, but they are burried in a field and I can't get out there to see what have unless I am going to buy them. Help please.
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