If my memory serves me correctly these Cadillacs had the VIN number stamped on the top of the frame right front. If anyone is concerned I have old manuals I can consult to make sure.
Glad to see I am not the only one doing this I have been doing the record keeping on 55 and 56 Packard Caribbeans since 1958 amazing how many still exist. Due to the cost these (the Cadillacs) were low production its a shame the info is not available as to how many were made.