Hmm.. Just done a little looking and found these ones..
Pure Grunt Hi-Performance Centre
81B Dixon Rd Rockingham WA 6168
ph: (08) 9592 8100
Kwinana Performance
South Of The River Performance Shop
10 Arkwright Rd Rockingham WA, 6168
Australia - (08) 9529 3636
I think you will find the best places are up around Perth for tuning and performance modifications, Hyper Drive would be my pick of the bunch, It would be a bit of a drive for you but would be well worth it, Ken is a Skyline nut and also sponsors this club!
Even if your looking for a normal service it pays to get it done by people that work on these cars every day. (Might cost an extra few $$ but its worth it.)
http://www.hyperdrivems.com.au/
Give him a call and see what he says! Nice honest bloke with an awesome reputation.