There should be no duplicates of engine numbers because the engine number's suffix is a production sequence number that is unique only for your truck.
The OP's engine number is F0620J which tells us it was built after 1956 (that was the last year Chevrolet stamped a serial number on the engine). This means every engine built in Flint on June 20th with a J code will have the exact same number... there's no way to tell them apart, so it can't be used for titling purposes... it's not a unique number.
Mike B
