Jim, Welcome to The 'Bolt.
I've seen many pics the past several years of earliers Aussie Chev trucks over the years. Most seem to have different door assemblies, even slightly different cabs. Your Dad's Old AD appears to also have Australian (New South Wales?) market specific doors. Looking closely at several of your pictures indicates window openings which are squared-off at the bottom, unlike our North American ones which have rounded corners top and bottom. The wind-wing (vent window) assemblies are different as well.
Judging by the size and shape of that front bumper and what's visible of the front wheels, that's a 1 1/2 ton flatbed. Bigger than the average half ton, but still one nice machine, well worth restoring.
Regards,
Wannabe
