My recommendations (Sydney)

If you're looking for a workshop in the greater Sydney area, my recommendations are:
 
- "MRC Dyno Services and Performance" in Castle Hill.
 
- "Advance Motor Mechanics" in South Strathfield.
 
Both of these workshops have done major work on my car and done it well. They are always happy to explain things and answer any questions you may have. They're not cheap, but that's because they're good. If another workshop does the same job for significantly less, then chances are that they're rushing it and not doing the job as well as they could.
 
MRC does most mechanical work in-house, apart from specialty things which they sometimes outsource. Mark from MRC is a very good dyno tuner and he did all of the tuning for my car. I'm very happy with the tune in my ECU.
 
Advance Motor Mechanics do just about everything in-house, including things like transmission rebuilds and wiring. The only thing they don't do is tuning, which they normally outsource to JEM. There are many VERY fast and reliable drag cars out there which were built by Advance Motor Mechanics and tuned by JEM.