Those are the ordering numbers and the numbers on the box, they are not the number marked on the shock. Keep in mind that there are no (to my knowledge) factory parts that had a "Z" marked (cast, stamped, etc) in the fourth position - C5ZZ-12345-xx. That "Z" indicates a Ford Service part number.
I found several listed original Ford part numbers in the Ford Car Parts book without applications but they all cross reference to the same service party number so they are not completely useful.
C4ZF-18045-C thru -G, C5ZF-18045-A and -B, all indicating a service number of C5ZZ-18124-E, Motorcraft AB-100. The heavy duty shock is shown as C6PF-18077-DY, the service is C5ZZ-18124-D, Motorcraft AX-99. These are all shown as replacements for 64-66 Mustangs. There could be Falcon or Fairlane shocks used as well on those years.
As stated above, this information only applies to the part in the book and what's marked on the box. The contents of an opened box cannot be verified.
Jim