I have done the CASA basic exams and the best advice i can give you is go thru Queesland Aerospace college in Brisbane
Queensland Aerospace College (QAC) - Accredited Aircraft Engineer Training .
At least give them a ring to discuss it . I think you only get the one chance to pass this so ask them that also.
YOu should know that the CASA exams are very old and unless you have been working on Connies , Electras and DC3 then you will have a hard time passing with self study