Howdy,
A couple of questions. Do you hold an Australian ATPL?
Forget JAR 23 aircraft. You want JAR 25 aircraft. (ie the ones you mentioned, such as the B737 etc)
What type do you have the 500 hours on? If it's a JAR 25 aircraft, then all you need to do is a LST in the sim. (It being observed by a CAA examiner)
If you go the way of a type rating, remember you'll need to have the LST observed by a CAA examiner. Believe me, organising that is a real pain.
Have you looked through "LASORS" on the CAA's website? it has all the requirements.
Also, the JAA site (
JAA TO - Joint Aviation Authorities Training Organisation) has all the types etc. It's a bit of a pain to sift through but it's well worth it.
Note, JAA is morphing into EASA so make sure you confirm every thing with the CAA.