Only some HQ Sandman is based upon Belmont, and trim is the same as whatever the base Belmont or Kingswood had. HJ works the same (except no Belmont of course). It wasn't until HX (after GMH had killed off the Kingswood Sandman) that Sandman got Kingswood spec trim as standard. So whatever seat material, door trims etc that came with a Kingswood for the trim colour selected, a HX or HZ Sandman got (unless it was over-ruled by the XX7/XU3 package eg horn button or dash facia). This is why black trim in a HX Sandman is 18V not 19V, as not only is Kingswood colours different, the vinyl is different. So is the name of the trim eg Black v Slate black, Beige vs Chamois etc.
So I suppose another way to view it is in HQ, ticking box XX7 got you either a standard 173 Belmont van/ute or 202 Kingswood ute with:

M11 (console)
M20 (4spd)
N66 (rally rims)
U21 (dash)
XS6 (buckets)
Some black paintouts.
Plus a set of stripes in a box, and on Kingswood deletion of the side and tailgate strips.

Essentially just a base vehicle with a few options. This is why Sandmans are impossible to pick in some circumstances (although there is one surefire way to pick a HQ or HJ).

You also got a choice of tyres, but if none selected you'd get whatever was standard for the base vehicle. The choice was also governed by the engine you optioned. Plus certain items selected added others eg selecting L32 got you a 3.05:1 1st gear 4spd, L31 got you a 2.54:1 1st gear 4spd.

Hope this helps.