Don't bother. you'll need new harnesses, engine, trans, clutch kit, shift linkage, center console, ecm, rear end, BIU, keys/fobs. Easiest and cheapest way to get STI performance is to buy an 07-09 spec b.
I already got a new intake, short throw shifter, catless mid pipes, and stainless works 3" catback on the goat. Vengeance racing VXR5 cam to come soon. maybe CTS-V calipers and some VMR V721 or TSW Mallory 19's. we'll see......
more like 5 nightmares with some fun in between. I saved at least 10 grand in labor doing everything myself, but I still wasn't looking forward to the next issue.
I sold it. Engine out 5 times, trans out once, $20k in repairs/mods. just had enough with worrying about the next problem. Figured going with my roots (V8 RWD), would be able to take more power with minor work. 400HP is a nice starting point, and if I add boost, the internals won't be falling apart until over at least 500 wheel. add in the same monthly insurance payment, saving $140/month on the payment, also a rare car, and 41k miles when I got it........yeah!
I had 8mm phenolic spacers on my 2.5i, and it was a bitch bending the EGR pipe. I did have a 30 degree farenheit cooler intake manifold temp though after. If you want an easier installation, go with the 3mm ones. shouldn't be as hard. also, specify to the manufacturer whether or not you have the risers on your manifold. some manifolds have long bolts, others have short.