Turbo for a GQ 4.2 Diesel

you could fit a 2nd hand one yourself pretty easily (there was something in the trader for $1400 - and people sometimes take them off of gu's when going for more power) these options will generally give you a turbo and manifold, then you need to make the exhaust fit - better to put a larger exhaust on (2.5 - 3"), make the aircleaner work - a lot of gq people use a gu filter which goes where the standard gq pre filter sits (behing headlight) set up an oil supply and return line, then get it tuned (ideal but not immediately necessary)
Other optiones can be added later.

Andy at dieseltec in lilydale has a pretty good name on the OL forum, and personally thats where i'd go - get the manifold and ball bearing turbo, fit and fabricate the rest myself, then take it back to be tuned.

Gas seems to work pretty well, but from what i've heard really compliments turbo diesels - probably better to get the turbo 1st then see if you need gas.

If you can fit one yourself, then your budget should be close to the mark.
I paid (from memory) $2900 for a kit from Turbo Glide in Russellvale, NSW about 3 years ago. My truck is a GQ as well, had 230,000k's at the time of fitting.
Click here for their site
It seems to me to be a damn good kit, it made a huge increase to the way my truck performs, particularly when towing. I paid another $2000 for fitting, injector and pump service and tune up etc. Wouldn't have a N/A diesel ever again!
If you fit one, make sure you fit a pyrometer and boost gauge and learn how to use them, very important for looking after your engine!
Hope this helps

My father used to run a four wheel drive specialist workshop in Brunswick Vic called SafeTrek and now teaches automotive at Box Hill TAFE, I could see about the two of us fitting one together, he might even be able to do it as an exercise with the students, I should make the most of my dad being a mechanic, even if I pay him instead of a company.

Keep your eye open on Ebay.I picked up a DTS kit(complete with manifold, airbox, all fittings and clamps) plus Intercooler for $1200.The turbo had lost boost(new that) and factored it into the buy price.Cost $500 for a full Turbo overhall