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I think you'll be fine with those upgrades. I don't have a cat and I have changed the muffler and it never threw a code. My suggestion on the exhaust would be to go to a local muffler shop and tell them what you want. Generally it will be cheaper for them to make the exhaust by bending the pipe then it would be to buy the kit. I got a good exhaust shop that does killer work at a very good price but I think its probably one hell of a commute here (CA).