Propane conversions are done everyday basically in Oz, and I've driven plenty of cars on either dedicated gas or dual fuel. If you go straight gas (LP that is) you can tune just for it and being the octane rating is a decent amount higher with propane you could setup just for it. Or go dual fuel if you still want to be able to run petrol as well. Just run the LP tank in the trunk (just behind the back seat would be a common spot) an go from there.

These guys http://www.lpgas1.com.au/ are around the corner from my buddy's shop and maybe you can read a little abit about the stuff on thier site, but will be tons of info and places that do it in Oz in general.