We've seen that park lamp set up before on Australian trucks. Someone posted pics of Aussie 48-50 trucks before and it was noted then that the traditional upper grille bar park lamps normally seen on North American models are replaced by the fender mount units. It's a "down under" thing. I'm guessing the Aussie government wanted marker lights closer to the outside edges of the truck, and not set so far inboard.

I'm going out on a limb and saying the stamped number you found on the frame rail, 9G12878, is your vin. It's consistent with the location, style and type seen in up North. The 7R8T number I believe is a part number for that particular piece of the frame. The vin is unlike the sequence used in Canada, but more like a partial vin used in US production. But the G is not a code I'm familiar with, and the smaller size is definitely unique. Very cool truck.