First up, you need to get your 'old' CAR 5 qualifications updated into the 'brave' new world of Part 61 speak. It's been a while since I looked at it, so apologies for some vagueness, but go to the CASA website and get hold of electronic form 61-9TX.
What you do is go through your old qualifications, and use the form to apply for everything you think you're entitled to. Log book pages with any sign-offs, the old sticky strips, anything that shows you were tested/checked/signed off for any qualification, are all gold, because you'll need to prove some things. They will have some records, but changes in rules and terminology will mean 'the computer says no' on some aspects, so whatever you have to back up your claims will come in handy.
When Part 61 came in, you could get an instructor to sight and certify your 'old' documents, which would then be sent in to CASA to get you your new licence. Not sure if that's still the case. You may need a JP or some such now, perhaps.
Terminology: Licences, ratings and endorsements are now permanent. Instead of a rating expiring, you need to do a Proficiency Check (for an instrument rating, instructor rating etc) with a Flight Examiner (like what an ATO used to be) or a Flight Review (basically a BFR) for general proficiency, low level ops, and a few others. Flight Reviews can be done by suitably qualified instructors.
That's not an exhaustive list, and it'll take you a while to get your head around the terminology. Strangely enough, aeroplanes and helicopters still fly much the same and you'd be spot on if you asked what the point of all this confused newspeak is, but that's another (lengthy) story.
Anyway, worth your while to track down that form, try to struggle through CASR Parts 61 and 91 for a starter, and get out to a flying school if you have access to one for a bit of ground school from an instructor who's current on all the guff. Good luck mate.
Edit: Sorry, I see you're in the UK - if you can track down some face to face with a current instructor in the Aussie system, maybe Zoom or whatever, that'll help cut through the crap, but you'll need to spend a while trawling through the books yourself unfortunately. On the positive side, all the regs are easily downloadable from the CASA website, there's just a ****load of them.