Hi Jimbo,
Check this out to start with:
https://www.casa.gov.au/standard-pag...rseas-licences
You will need a CASA Aviation Reference Number and CASA initial Class 1 medical to start with. For a CPL conversion you will need to complete a Human Factors and Air Law exam then complete the necessary flight training (as deemed necessary by your chosen flight school) and undertake a flight test with CASA designated examiner.
Then the fun starts.... for an IR you will need to complete the IREX exam and then you will be required to take the necessary training and flight test (excluding sim hours) in a ME IFR capable heli, this will give you a CASA Command Instrument Rating.
There is plenty more to it, lots of differences and nuances, for example like the way there are a multitude of ancillary ratings and endorsements that just don't exist in any other regulatory body.
But with your experience you might just find the right company in Oz to do all this for you in-house if you're lucky.