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Before you pull the pan make sure that the knock you hear isn't a ping from running too advanced.

Try running the spark lever a little bit at a time less advanced to see if the knock gets less or goes away.

Do you know if the engine has a high compression head? If it does have a high compression head running the spark advance as if it was a standard compression head will almost certainly cause it to ping/knock.

Pulling the pan is a fairly straight forward project but putting it back on correctly to eliminate leaks is a bit more demanding.