Kev, I used to live in Adelaide and loved the Bathurst races especially when there were so many different makes and classes in it. The RS 500s at the time were set up for racing and I expect the guy you spoke to will be able to let you know what bodywork modifications are needed to be able to fit the extra wide wheels and tyres you want. You could go all out and make your car look like a racing RS500 but you will need a fat wallet!