John,
I am not familiar with the Holden body Chevrolet. interesting that the parts transition is different "down under". Thanks for the history lesson. Makes you wonder what else may be similar but different.
Have you examined the radiator support and the connections to the fender/fender well? You could possibly eliminate some factors by parking the truck in a level area, and jacking up the front of the truck equal heights on each side supported by the frame. This hopefully would eliminate differences in sagging springs or other suspension irregularities.
Also, have you removed the bumper and stacked the brackets on top of one another? If they are bent, the difference should jump out at you.
With some persistence, you will figure it out.
Paul
