That is an early HZ XX7.

HX-HZ XU3 is the normal Sandman. Sandman started out as option code XX7 in HQ as a sports commercial, basically a ute or van with SS nose, a few blackouts, buckets, GTS instruments, console shift and stripes if you wanted them. Towards the end of 1975 GMH changed the Sandman package option code to XU3, and introduced a second package which adopted the XX7 option code. The second package had passenger tyres on it, hence the load carrying capacity was reduced. This means the vehicle's gross vehicle mass/weight (GWM/GVW) also reduced. The XU3 package could carry 14.5cwt (approx 750kg) and the later XX7 could carry 10cwt (approx 500kg). This is the reason for the 250kg GVW difference between a normal HZ V8 van or XU3 (2200kg) and an XX7 van (1950kg). In 1978 the HZ XX7 van's GVW was changed to 2000kg for some reason (haven't found the document that tells me why yet).