According to the EPA you cant run an older motor in a newer model car, unless you want to pay $ to get it pass EPA regs. (NSW & QLD)
If the engine number is an Rb30 one it will be rego'd as an RB30, regardless if its twin cam or not.
How does it work in QLD? You stamp your engine number on the RB30 and keep it looking stock, thats the easiest way.