Scott's van is a new one to me. It probably isn't the last HQ Sandman, but it'd be in the last few. I have another Elizabeth HQ van (non-Sandman) recorded later with chassis number 61494, body 126015 and PSN L286254. Unfortunately GMH have no HQ Elizabeth records past about July 1974 so we'll never know how many HQ's were made at this time at Elizabeth.
I do know that the first completed Elizabeth HJ is a 202 3spd van completed on 16/9/74, its PSN is L286623, but by no means the first Elizabeth assigned HJ PSN which is L286435 - a 202 4spd cab chassis (possibly the HJ brochure car).