You may already know about this, but a lot of our orders and regulations are on the web at
www.casa.gov.au, so have a look there.
For the conversion of an ATPL (H), for example, apparently you have to sit an overseas conversion exam, which I don't have details of but would imagine it's air law oriented.
Have a look at the Civil Aviation Orders (CAR 1988), Section 5 Reg 5.174 and 5.181 as a start point.
I think it is possible to sit exams outside Australia, but an email to CASA with a query would give you the (hopefully) correct answer about that.
The web site mentioned above is quite good - CASA cops a good deal of slagging over here about various things, but they have done a good job with this site at least!