I thought the first set of cats was a fairly high flow design. I would ditch the second set, and use a slip on style pipe with stainless band clamps for install. This way the purchaser only needs to cut the factory exhaust in the same location on each side and slide in the new one. This saves the trip to a muffler shop along with the additional cost. If the factory cat are not worth keeping then go from the headers back. Since you are mocking up sets why not have two options available full and catback.