Yes you have to install a "cat" back into the system to make your truck "street" legal. You will have to make sure that the new headers meet emission requirements too, such as having ports for the air tubes for your smog pump. Do you have to have your truck emission tested ? Here in Illinois they will sometimes check under the hood and truck to see if anything is missing or changed from what their system ID tells them to look for. (such as missing converters; air pumps & tubes etc.) Find yourself a good legal header and free flowing converter & exhaust system, you'll save yourself a few headaches down the road.