after having trouble with the cops doing this a few weeks ago, just keep this in mind if buying a car from VIC without roadworthy. the owner keeps the plates, so you have to get a permit to drive the vehicle without a roadworthy. GET A SINGLE TRIP PERMIT, not the other option which is to take it to a mechanic to get roadworthy done. the fine is $500 if you get caught (driving unregistered vehicle) and then you need to spent another $50 for another permit, which is the same as the first one with a differen box ticked.
also, even though transport SA will tell you otherwise, the SA Police WILL NOT recognize the victorian unregistered vehicle permit, so get an SA one before you go.
be nice if they agreed seeing as we had a form filled out ready to get the SA permit, but upon taking it in, they said it was a waste of money and the VIC permit would suffice. towing a car back from SA/VIC border @ 70km/h is not fun.