Unfortunately unless it is a Brisbane build with XX7 stamped on the body plate, or you have the original build sheet, or you have the original vehicle identification certificate there is no way to prove a HJ is a genuine Sandman.

Your HJ appears to have all the Sandman identifiers so the best we can say from the info is it is most probably a Sandman.

Trim 1888-64 ............. 1888 is the exterior trim colour- Cotillian white............ 64V is the interior trim colour- Gazelle

From the pictures there is not much original HJ left on the car, mostly HX and HZ. Very nice looking van though and the main thing is that you are happy with it.