HQ80480 = V8 Kingswood Ute
568 = *Solid Colour -15894 = Burgundy *I.E: Not metallic.
Trim 30 is long grain Black vinyl. E = Kingswood Trimmings?
TRANS: M20 = 4 Speed the fact it has nothing in the ENG and AXL is because the running gear is factory standard for the model. 253ci V8 with 3.36:1 diff ratio
M = Dandenong, Melbourne, so it will NOT have XX7 stamped.
3/74 is the right build period to be a Sandman.
8N = Kingswood Ute 80 = GM Australia R = High Compression 253ci V8 D = 1974 J4 = Dandenong 20457 = Serial Number Q = Model Series Code.

Nothing to say 100% it is a Sandman but all the pointers are good (except the "E" in the trim code) which I feel is probably fine but Blocker seems to think it must be a "B".
I have a feeling Kingswoods were 30E and Belmonts were 30B.

I'm not saying your Ute is a Sandman but I'm not discounting it. More points to it being one than not.
We would need to see photos of the body. Console mount, shifter hole etc.