Near the end of the HZ series GM Holden had decided to cease the Sandman ute, and only speculation can point to the reasons. Most likely the new direction of the designs or sales figures pointed to a reduction in the recreational vehicle and focus on larger commercial cars. There were plans to continue the Sandman panel van into WB as early as 1980 but by the time the WB was released there was no Sandman van or ute much to the disappointment of many Sandman fans.
There has been much speculation (myth) of a WB Sandman, but it did not exist. It was not produced and if anything a mock up was created from various parts, but there are no records from GM Holden that one was produced.
Below are scans published with courtesy of GMH.
Proposed Features and Styling
An excerpt from the WB Production Features Manual, marked Obsolete. The WB Sandman would have been a van only with a base option of 253 and 4 speed manual - nothing particularly different from the earlier models, the only notable addition we can see from these documents is the addition of cloth inserts in the bucket seats.
The production development did not even go far enough to provide further details before being cancelled, you will see that the documents are dated August 1979, proof the WB Sandman was killed off before the end of the HZ.