The F56X looks like the engine serial number suffix in the same format as for '54 and '55, so it would not be a date code (similar to casting date codes) as translated by red58. I think the engine serial number format changed for '57 to include the date code (with the month as 1 or 2 digits, and the day as 2 digits, and no year). If I'm right, F=Flint engine plant, 56=model year, X=type code=235 from 3100 series. So your engine is a '56. Was there a sequence number stamped before the F56X on the pad by the distributor?

Curt
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1953 Chevy 6400, 1957 Chevy 2dr Sedan
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