ian, you'll be after a set of gt-ss. however i doubt ull want to pay for that little HKS badge, so go and have a talk to dan, he's supplying my turbo's for me.
Another thing is to go and look at the dyno thread in forced induction (its a sticky) as there's a fair few setups and figures in there.
Youll be look at ~3k for the turbo's, then u'll prolly want to change dumps while they are off, and then u need gaskets.
On a side note, give me a figure ud be willing to pay for my N1's and i'll think about it. Also i'm selling those hks dumps, and the trust front pipe.