Confusing HQ Van

[Rockape]

Hi all.
Have just bought a HQ Van that I did not really want but the price was right and it is all factory, never been pulled apart, and is complete. It has quite a bit of rust but by no means the worst I have seen. I bought it based on the build plates which read as follows -

Model - 80270QR
Body - 793876-S
Trim - 1854-30B
Paint- 563-15345
Eng- L31
Trans- M21
Axle- GV2

Build Date- 11/73 ( CONFUSING )
DHQ XXXXXX
4850 LBS
Seating Cap 2

Vin- 8M70T *D* H7XXXXXQ

Ok, the van is completely stock by the looks of it and is a 5 litre, 4 speed, 3.36 LSD, factory air, GTS instrumentation, factory HQ buckets and centre console. Am told the factory colour is Dulon Mustard, this colour can be seen all over the van under the new paint.

Now, the conundrum. Build date of 11/73 BUT D in the Vin signifies a build date of 1974. Any ideas?

The seller tells me an interesting story. He tells me the guy he bought it off was a painter at GMH and he believes the van was a proto type/demo for the coming HQ Sandman range in '74.

I'm curious to know what you guys think. The D in the vin has me excited, but the build plate clearly identifies 11/73.

Everything else is right except for - It has a twin headlight front and the wiring looks factory. It does not have fluted guards, but this can be easily explained.

Thanks in advance guys.

Edit- Engine No- QT673544