Mr T,
The Aus IREX is a three and a half hour written examination of approx 40 questions requiring a 70% pass.
The Bob Tait book is great but you
will need to have a close look at the AIP ENR 1.5 (know it back to front) as well as the CAOs 20 - 92.
(as much as I hate
ASL, their website lists all of the other ref documentation required for the exam).
Best of luck
Lockers