"Does anybody know exactly what would be required to get it registered in Aus?"
Here in Oz, with a trike you can go with either HGFA or RAAus, your choice would probably be based on whether you wanted to also play with Paragliders & Hang Gliders (HGFA), or have a view to converting to 3-axis U/L's in future (RAAus)
Brent, I suggest you drop an email to each. Conatct details can be found on their websites.
http://www.hgfa.asn.au/
http://www.auf.asn.au/
Rgds,
Glen