Dunno if it's the same down there, but for the hill climb at Mt Cotton, Brisbane, you don't need a cage or harnesses but do need a CAMS 2S license, battery triangle, tape on headlights and any other forward facing glass, 2kg fire extinguisher, helmet, neck to wrist to ankle non flammable clothing (no nylon or synthetics, cotton or wool only), shoes with leather uppers and working seatbelts (not frayed and must lock when yanked on hard).
And a 3rd party extension for the event if the car is registered.
If its run under the CAMS regs, then its probably similar to the above requirements.