bro i have done this mod to my rex and what you do is just gut as is. dont cut pain in the as.. the best thing is to take your time to really get all the cat shi... use a drill bit you dont care about and a peice of rebarb works well also a good shop vac. make sure you get all the cat out if you dont it it may spool into your turbo and will cause some probs. so take your time and a hint use a wire brush it works. its a bitc.. but its worth it.. also do you know about the resistor mod.. if not run a search.. good luck