NSW can be a pain in the butt to get anything registered.
Recent law changes can make it hard in this area. AFIK the back wont be a problem, most of the rules relate to the bull bar, and how dumb asses who walk in front of your car may be injured by it.
Mainly the laws relate to things protruding past the front of the vehicle, so in this area winches may be a problem. Having said that there are plenty of trucks running around with them on, it will all depend on the inspector you get. The reason you probably havent seen any in NSW, is the high poser factor, especially in Syd (socer mums).
Im sure there are others who may be able to be a little more specific.
You may be in luck in that its already fitted to an older vehicle.
Best be would be to try and get it passed as is, then if it fails, see what they want you to do.
ARB have winch bars which meet the new rules.