Sandman XX7 van alright. I'm not convinced it is exactly a nice colour on a van, maybe looks OK. Possibly DY4 stripes? Might look better DL7 if you are planning on using the original colour, although the stripes might liven it up a little like they do with atlantis blue.
The N67 wheels on that HZ Premier in Leroy's link are what your van would have had when new.

It is also one of the last HZ Sandmans I have recorded with the old trim codes. There is 1 x HZ Kingswood van with V code trim I have that is 12/78 but November is the changeover month (the 12/78 probably got held up by something stopping it's engine and chassis coming together hence got a 12/78 date, it was probably started in 11/78).

Your original engine may also be one of the last of the HQ series engines, if so it will very close behind QR999999. Depending upon when in 11/78 it was built it may even be a very early HZ series engine, something not much higher than ZR1001.