could be bad news.
to register an engine swap, first you need a receipt for the new motor.
then, you'll need to prove that it was available in the same body in an australian delivered car, and that all the emissions gear is the same.
if this isn't the case, you may need an engineers inspection which can be costly, around 650 dollars.
if the seller notifies vicroads of the new engine number before you buy it, you may be able to get a roadworthy and transfer it to your name without any hassle, but this is not failsafe.
all the best.
-dave
also has all the info, but sometimes hard to undrestand.