Mick,
It's a poor quality image but I think I can deduce the following:
(1) The truck, with visible registration '1905' or '1906' of '1965': these all correspond with RAAF serials 201905, etc, and are a group of Chevrolet 160inch WB 'Truck, Heavy, GS'. The chassis serials are all '4215Mxxx' so are Series 15, 3 ton, 4x2 Chevrolet built in Melbourne at Fisherman's Bend (the 'M' in the chassis serial). The guards are the high cut-out type military type, so this truck is most probably fitted with 10:50x18 tyres on two-piece rims.
(2) The Blitz is most probably an F15 - the registration visible has a '1' as the fourth numeral, and only one group of CMPs that falls into the number sequence 20x1xx are F15. So a 4x2 Ford F15.
(3) Unit Sign: the only RAAF possibilities in the NT that I can find are 613 or 617. From the shapes, it appears to be 613 which was 61 Operational Base Unit. The background colour to the plate was Sky Blue.
Regards
Mike