Howard,
I did a couple of years ago exact what you are wanting to do:
you need to do all CPL-H exams, aerodynamics-H is a bit of a pain for a fixed wing person, you'll work it out.
The theory ( including ATPL-H ), accept no substitute, go to see Warren at AFT, they are fantastic.
School: i'd suggest someone like Fleet Helicopters at Armidale, there was a top bloke ( well for a
VB drinker ) Tim Latimer was rumoured to be starting/started a school in Byron Bay ( or near by ), or HTT at YSBK.
Do not go to one of the sausage factories.
Rotary is a lot more fun than fixed wing, enjoy !!!!!.