It should fit as it is basically the same size as one from a GTS-T, or just knock out the one you have(which is illegal). When i replaced my std exhaust, a previous owner from japan had already put a hi-flow cat in. Sometimes you don't know what you got until you look!
1, which ones should bolt on without modification, r32, 33, 34? (R33, not sure if R32 R34 would fit)
2, any ideas on cost? (Depends on who you know)
3, any other info or suggestions? (not really)