I hear very good things about Louis Giossis of Motion Automotive. My '76 has been there many times, but before my ownership. I get my 911s worked on by a family friend who is a retired Porsche Tech. In fact, he owned his own shop and retired young. He does tinker work at home to keep him busy. My '89 was predominantly worked on by the Porsche Centre Melbourne, prior to me getting it.
Fitzgerald Racing Services is also a very classy operation. They also specialise in regular maintenance etc. There are quite a few guys on this BBS from Melbourne. They'll chime in soon, with their recommendations, I'm sure.