http://www.rta.nsw.gov.au/registration/getnewrego/interstatevehicles.html
thats the link regarding what you need.
when you say pretty much stock, what mods have been done? Have a look under the car and make sure there are no hidden suprises (e.g. de-cat pipe)
When i went through it, it was basically the same as renewing the rego, but you needed a blue slip too. (It was my daily, not the the gtr)
Ensure all the complience plates are on the car and the engine/chassis number match what the car has. (as was mentioned before, you may need to supply original complience paperwork)