I dunno man, if you strap a turbo to the GTS that is putting out enough boost to make 400+ HP, I don't think the motor would last too long, not stock anyways. The compression is too high, boost levels would have to be conservative.
That setup would be their stage 3 setup, the engine work is required to lower the compression & beef up the internals. I wouldn't run much boost on a stock 2ZZ, you get a big kaboom!
The intercooler would help, you could run a boost level a little bit higher when intercooled, but for the 2ZZ to make power, you'd need dished pistons like the 1ZZ has (there are nice aftermarket 1ZZ pistons for this purpose, they will fit the 2ZZ block when used with 2ZZ rods)
Valvetrain would need to be beefed up a bit, forged main caps too.
BTW, the tranny will be okay, so long as you add a racing clutch & flywheel, and upgrade the CV axles to stronger aftermarket units. (Try http://www.islandmotorsports.com
, they distribute Enjo cv axles that can handle that kind of power, You would need stage III axles, they're race-duty rated at 275 HP and up)