Old australian racing regulations?

[ford man xf]

Before todays v8 supercars, the older australian touring car championships, what where the regulations if anyone knows? For example, the cars that where raced at Bathurst, Phillip Island etc. the cars there, they where the exact models you could buy off the showroom, for example, XY GTHO that where raced, you could buy that same car in the showroom, had same power handling etc.? And the manufacturor had to release at least 300 to showrooms to race?

Then in later years the rules changed that for racing that the racing versions could have 15-20% power increase over the showroom model?

Is this correct?