I live in NSW and just got my 71 registered about three weeks ago (finally). I don't know what the true laws are exactly, but here is my experience. Regarding conversion it must be older than 30 to be exempt, which is OK anyway because big blocks are all over 30 and I am assuming that everyone would only really consider a big block ;54
Seriously though, If it is newer than 30 and older than 15 you will need to have it converted and the engineering certs to go with.
Your ticket to registration is a blue slip which is essentially a very comprehensive safety inspection. Once you have your blue slip you can bowl up to your local RTA also with your import approval papers. You will also need some sort of proof of purchase/transaction. With these in hand you will be up for 3% of the cars purchase price in stamp duty, the registration fee (a couple of hundred) and the cost of the licence plates (varies on choice).
The sometimes tricky part with a foreign car is getting the blue slip, as this is the inspection that will determine your cars safety and compliancy to applicable road regulations.
I checked high and low prior to registering my car as to what the legal requirements where for my car to be compliant with all applicable rules/laws. After long searching I pretty much found nothing. I have heard people say you have to get the lights changed etc, but nothing ever definatively concrete. So I rang the RTA and asked them what I needed to do to comply my car, they told me to speak to the inspection station who would do my blue slip and they would tell me what I needed. So I rang a place and they told me to check with the RTA, I rand another place and they told me the same. I rang the RTA back and explained to them that it would appear they where the ones who help my information and was told "no, it is the inspectors job to determine what needs doing" So I ring another RTA office, and guess what..... Once again, they can't tell me.
So I pretty much came to the conclusion that nobody really knows sh#t, other than the general vibe that if it's over 30 years old nothing seems to matter.
I have spent pretty much the past 18months getting my car up to scratch so everything was clearly safe and roadworthy, yet I had made no changes to lights/seatbelts etc when I took it for my blue slip.
When the day came I drove it to the inspection station where he checked it over etc, etc paying only attention to safety/roadworthyness and gave me my blueslip.
I then walked into the RTA, presented my documents and ten minutes later walked out with plates and a rego sticker. I have heard that the RTA take 24hours to do an independant check on the import approval to accertain it's authenticity, but the lady didn't blink twice.
So all in all I think I was probably luckier than some as the whole thing seemed a little too easy. But ultimately I think it really depends on the people you find yourself dealing with and their knowledge of the rules/regs.... which let's face it, when it comes to old cars like these..... everyone is pretty clueless.
Anyway, that's fine with me because now I can get in my Vette and drive...... And despite all my efforts I don't think i'll ever really know if it's truly "legal"