I have a 'frankenmotor' set-up myself. 2.2l phase 1 heads with Delta Cams on a new 2.5l STi shortblock. I use the Cobb EQUAL length headers that are JetHot coated w/ the Random Hi-flow Cat. I suggest you locate the OBX knock-offs on EGhay as Cobb no longer makes the headers I have anymore.
BTW, You'll love the torque and the fact that it pulls all the way to redline