air-cold water is going to be pricey, big and complex unless you build it yourself, and it will still take up lots of space and be complex and still cost more than an air-air unit. I built one for drag racing. It is hands down the best style intercooler for drag racing, but it ain't cheap or simple. For a street car, air-air is probably best. Heads - performance heads will definately help make more power. Do GSRs have aluminum heads stock? if they're iron, then aftermarket aluminum heads will help a lot. they allow more boost by dissipating heat much better than iron which prevents detonation.
As for my recommendations/predictions:
can't really help on cam specs too much, since I dont know valve sizes/port flow #'s for the heads... But based on my educated guesses, this is what i recommend:
Intake:
centerline : 110* ATDC
duration @ .050" : 205
valve lift : .442"
Exhaust
centerline : 116* BTDC
duration @ .050" : 210
valve lift : .476"
113* lobe separation, 3.0 advance
I estimate 219 ft/lbs @ 4750rpm, 262hp @ 7250rpm
For a turbo, I'd say a T3 "50" or "60" trim... I'd say a .42/.48 A/R t3 may be a bit small and restrict top end a bit. a .48/.60 would be better. These came stock on the late 80s Ford Thunderbird Turbocoupes, and can be found frequently on ebay. Here is a new one on ebay :
http://cgi.ebay.com/ebaymotors/ws/eB...tem=2467730367
38lb/hr injectors, 40s are more common and would be best bet in case you ever want to increase boost.