the dark colouration made me think Ingram's was a possibility. Quite decomposed roadkill
ID confirmed by Jonathon Lucas, who said "The narrow head, neck flare and general build of the snake immediately points to a brown snake. Mulgas will flare their necks like that too, but their head won't be distinct when they do it, and they're much heavier bodied.
The only other species of Pseudonaja that flares like that is a speckled brown and it's definitely not one of those, and is too big to be one of those too. Reticulated pattern is also a clue."