You do know there are more mods than just that needed right? Where's the fuel delivery system? Logging/tuning devices? I wouldn't trust that turbo kit for shit. Are you any good at working on cars? You can have a DIY turbo kit for about the same price that will work much, much better. That T3 turbo is probably glued together and will roast the hell out of your stock block, the BOV is probably a fake POS like the rest of ebay's turbo kits, intercooler looks like ass, a sidemount will do fine for that, and the wastegate looks like something I could make from wood.
If you're really interested in turboing your GS, take a look at this.
http://www.2gnt.com/index.php?d=GSGo...%20Turbosystem
I know one of the members on here turbo'd his GS, you could probably ask him exactly what it entails, his username is SilvrEclipse.