It looks like you should be able to just hook it to the fuel cut solenoid wiring that should already be there even on a truck setup for manual choke. (72-74) It will be the black/yellow wire on the connector that did/does go to your carb. (On the firewall right behind the carb) The auto choke should have 12v power when the motor is running optimally, or with the key on if nothing else. If you hook a test light or multimeter to that BY wire it should have power only when the motor is running I believe.
Its been a long while since I've dealt with a pre-76 style motor, and never have had to deal with one not wired for an auto choke. That should be the closest wire to what you want. The alternative would be to hook to the coil's power source. Trace off the + side of the coil, you should find two wires that lead to it. One goes straight to it out of the harness, the other comes from a little box that is the resistor. Hook the choke onto the side of the resistor not connected to the coil and you'd have a 12v source hot only when the motor is running.
The choke just needs power to pull itself off after the right amount of time. Power it from the key if you have to, just like you would a radio or something. It will otherwise just tend to stay on, which you probably already are dealing with.
Hopefully that Aussie truck of yours isn't too different in the wiring scheme and all this should work.
