I donno man, depends what state you are in and what engineer you goto.
I used to ask people similar questions on forums and there is really little point to it as there are always gonna be a difference in what one engineere rekons is safe to another. also, its very differnt from state to state.
there is a page on the RTA website that has a list of all the registered engineers in australia. go to that, and start calling people in your area, they are more than happy to help (normaly)
also, jsut another thing to consider, later on this year the modification rules are goin to change all around australia (i think? or is it jsut nsw? ) which will make mods to cars a lot f*kin harder. try and get it done sooner rather than later...
hope this helps (i might have confused myself with some stuff, im jsut goin from memory)
-Tom