For Exhaust, I have always gone to Glenn @ Roadway Exhausts, Belconnen. Good work, Very cheap prices +REP
I once went to 'The Exhaust Shop' in mitchell, to weld a crack in my dump pipe and re-sit the exhaust,
It cracked again a week later and they wouldn't come to the party.... neg REP
For Tuning/Dyno, I went to Kit @ Gentech in Mitchell. He knows his drag stuff....
I reckon he did a good job, but I have nothing to compare it to. It cost $800
I used M&A Engeernig for my custom g/box mount and custom tailshaft. Did a top quality job, used all NEW parts, but cost $1050. +REP
For Smash Repairs, I use Braddon Smash Repairs. Did a great job, and was a good price.