unless there's something seriously wrong with your car, you'll make it on one tank.
just feather the throttle slowly going up hills instead of flooring and you'll be fine.
I drove to geraldton in june (via coast rd).
If i can make it from duncraig > geraldton on one tank (60L) with a carb that hasnt been kitted from new, no injector cut off on decel/ o2 sensors etc then you should be fine or your car has problems.