How can you make the terrain look aussie and not like thewild west ?? Any suggestions??
Kangaroos and koalas mate. 
Don't forget the Drop-bears and Hoop-snakes Frank, or the big spiders!
But it depends where you're gaming Marcus. Perhaps a more red ochre if doing a 'desert' style outback town, so pretty similar to American OW, but with corrugated iron roofing/walls (no shingles). But you will find the Kelly Gang was in the "high country" region of Victoria, so plenty of trees, log cabbins, and again a plastering of corrugated iron for good measure. Some wild horses and sheep stations would be another step in the right direction.
Colour: avoid green. Our country has big blue skys, and the vast majority of native vegetation is a silvery olive to browns.
The 1800's saw a fair amount of technology/building/engineering from both America and the British Isles, so feel free to mix and match

American stage coaches, and Baldwin Locos were happy operating alongside UK police and scottish steam engines.
Cheers
Matt