Wow.... that is a good one.
I think you have to comply to the Euro standards which have to have a running / brake light dead center on the back fender (that's easy, toss on a Sparto taillight.) and I think you may have noise requirements.
Until an Aussie Knocker speaks up, my advice would be to go to your Department of Motor Vehicles (assuming it's called that in Australia) and get a list of their requirements for home made bikes.
Somebody at a local bike shop might be helpful and give you a heads up on it.
As far as registration... I live in the States, I'm not even going to pretend to know...

There's got to be somebody around where you live that has a chopper shop or has a registered bobber / chooper over there that you can ask. Just keep an eye out for somebody who is on an obviously custom bike and see if they'll be helpful.
Good luck man, keep us posted! I imagine a few of us would like to know and any Aussie that wants a Knock in the future will NEED to know.
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