An H-pipe for Shorty Headers will NOT bolt up to a Long Tube Header. However, depending on what state you live in, take that H-pipe and your car to your local muffler shop and they can cut off the front part and should be able to attach it to the back of the Long Tube collectors. The reason I mentioned "the state", here in California, Long Tube Headers are not "legal" on street driven cars that were built after 1965 (such as a FOX chassis Mustang), while other states may not care. Muffler shops in California are very cautious about working on "illegal" cars, for fear of getting nicked by the government. On the other hand, race cars are not a problem. Although I'm not suggesting that you or anyone else does this, I had a friend that rented a trailer, loaded his Mustang on it, removed his license plates, and told the muffler shop that it was a race car. He had even gone to the trouble of using some stick on numbers on the side windows. When he told me about it, I could not believe that the muffler shop didn't know what was going on, but I guess they felt that they could cover their behind in case they got pinched by the state...