It has been my experience that the ’62 Jetfire engines have stamped numbers that begin with HHI, e.g. HHI 304490 or HHI 339111.  The ’63 Jetfires had engines stamped with JJ, e.g., JJ 292 or JJ 454.  Not sure of the significance of the “I”.  The ’62 numbers following HHI tend to be higher than the JJ numbers for the ’63.  May have something to do with the fact that the ‘62’s didn’t come out until later in the year.  Take a look at your numbering.  You may find a ’62 engine in a ’63 car!

jetfireman