FAA CPL to CASA CPL = Just has to do CPL(A) Flight rules and air law, meet min CPL experience req, pass a CPL day VFR flight test (check ride).
FAA IR to CASA IR = Check ride, IREX (written exam), meet min IR experience req (time in your own country counts). NB A CMEIR (Command Multi-engine instrument rating) allows you to fly single and multi a/c IFR. Only one check ride in the twin.
FAA ATP to CASA ATPL = CPL and ATPL written air law exam, IREX and IR checkride. The exams have to be taken first as you need to have a CASA CPL to do the IR check ride. There is no check ride for your ATPL.
NB. You are exempt from having to take the IR checkride and written exam if at any time you have had a CASA CMEIR. You are also exempt from the CPL air law written exam if you have held a CASA CPL before.
Im planning on coming back soon so have looked into it. Only thing I can't find out for certain - some of the majors may want you to do all 7 ATPL exams if you are converting from FAA regardless even though CASA doesn't require it!
Hope this helps!