What is your goal for the car? Peak numbers, big power? You state you want the GT30R, thats a pretty powerful turbo, but a little laggy especially running with the 2.0. Plus if you get the rotated your up and down have to be changed I thought cause of the new location of the turbo. There is a member, Lil Shoaf, that runs a gt30r. He has extensive work done to his car to include the engine and tranny. Look around and see what its going to cost you, and what your goal(s) is(are) and go from there.
"2007 WRX- PPG'd, 20G- Tim Bailey tuned
Stage 2 2005 WRX