Im in a related field. If u can pass inspection and OBD 2 tests, startup will be your only issue. The cat needs to be as close to the collector as possible, and the header needs to be wrapped and or coated. BUT... If you cat is already hot, that will help alot, so wrapping the cat will aid. Only problem is as stated a few posts up, you modified the system which EPA/CARB frown upon. Tuning for a lean startup to heat the cat faster will not work (dont know if its even possible), because your CO2 an NOx will be higher then the normal tune and the cat wont be warm enough yet to convert it.
ST Crew #90