You can bring an AT into Australia no problem Without having to modify it at all.
You cant however bring a vehicle in to import it under a carnet as you have to get an import aproval from Canberra before it enters the country otherwise you will be made to send it out to import it. It happened to to me.
It would be cheaper to buy one abroard aswell as i know a guy who works for a Honda dealership and Honda said it would cost $15,000AUS to get hold of one for him with average mileage and condition.
I only had to pay $550.00 GST to customs to bring my bike into OZ.
Look into it first before bringing a bike into Australia though before you are turned away with it. RIng customs in Canberra and they'll put you on the right path.