ok i have a flowmaster muffler now. i am thinking of changing my exhaust system completly. i want to know if i go with a full race header will the flex pipe still matter. i am thinking of doing a 2.5 focus sport flex with the 2.5 True Bendz cat back, and borla muffler. ( my flowmaster is very loud). if i start with the flex pipe first will it bolt onto the stock pipe??