just throwing it out there but would you not be better off getting a new garret 2871r as they can be got reasonable enough new and at least with a new turbo ya know what you have.The .64 exhaust housing is a savage bit of kit as you will find a gtrs laggy enough and your just paying for the hks badge
i'm fairly sure a gtrs is nearer to a 2871r .86, i could be wrong tho
I don't think so lad, they pull very similar figures on the dyno. Almost 100% they are the same as a .64 except that the GTRS has the wastegate hole already ported.