I hate to be a killjoy but judging from the photos of your antitank gun I would have to say it is a mixture of a British army type and the Australian type. I base this on the British style ammo rack mounted behind the shield.
These racks are totally different between the two and the Aussie one does not have the leather tool box sitting on top of the ammo boxes either.
I believe the Australian Army used both types and this shows in some of the AWM photos Tony put up.
Still a nice piece and I wish you well with it's restoration.
Cheers
Cliff
