The 3500HD or P30 and similar chassis came with the 10 lug on 7.25" bolt circle, and these trucks came with 19.5" wheels. There's nothing really wrong with them or the bolt pattern unless those 19.5" wheels don't exist in Australia.
You may look into the Ford front end parts, but when you're done I believe you'll find the later model GM I-beam axle components, either 8 lug, or 10 lug, to be much more suitable. Again, these parts swap to an old GM axle with 1.109" kingpin by simply reaming the bushings already in the newer spindles and fitting replacement stock 1.109" bushings inside them.
The Dodge 3500 rear will be very wide.
If you choose the 8 lug for your front hubs also read up on the 14 bolt rear axle upgrade. The P30 and similar chassis with 8 lug I-beam front axle and disc brakes (a good donor) come matched with an 8 lug GM 14 bolt rear that is much narrower than most other dually rears, a perfect width for these old narrow trucks.
https://www.stovebolt.com/ubbthread.../14-bolt-axle-swap-info.html#Post1249600
