There is no Sandman model number. It's a process of proving and disproving.
Understand a "Sandman" is simply a factory option pack on a Holden or Kingswood. (This Ute is a simple Holden).
Unless you have a Brisbane built Sandman with the actual tag stamped with XX7 or XU3 it is not an easy thing to confirm.
To go further with this Ute we need to the information of the other TAG with seating capacity and build date.
Then tell tale signs with the console mount and other body indicators. (Log Books or purchased order form help!).

Whatever the case this Ute is a long way from what left the factory.

Byron "might" help out with the info from the build number. I'm sure he'll join in when he has time.