Don,
The Australian greatcoat is virtually identical to the British overcoat - (Vallejo English Uniform with a drop of Olive Green always works for me).
It's worth noting that following the disaster at Gallipoli, the ANZAC (Australian and New Zealand Army Corps) Forces were reorganised into two Army Corps, with bulk of the mounted troops remaining in the Middle East to fight the Turks as part of Gen. Allenby's Desert Mounted Corps, while the bulk of the infantry moved to France in April 1916 to join the British Fifth Army commanded by Gen. Gough.
At this point, some of the original leather webbing was replaced by the standard issue canvas webbing issued to all British and Commonwealth troops (although you always see the odd exception). As the war progressed and the original ANZAC's were replaced by new recruits, the personal equipment of the Australian soldiers in France became more standardised, as it all came from Fifth Army Q stores in France, and not from Australia.
The distinguishing features of Australian soliders in France were;
1. They wore brown leather boots, not black;
2. Behind the lines they favoured wearing the Australian slouch hat instead of the Field Cap;
3. The distinctive unit colour patches on the upper arms of their tunics representing their battalion and division; and
4. Their unwillingness to salute British officers