Whoa, do not use MAC Longtubes on a Cobra. The reason, they scavange too much and they will suck the valve seals right from the motor and that will lead to excessive oil consumption..(buring of oil). The second reason is the inside of them are not smooth. They have weld deposits that loosen up and can go into the motor and damage the engine. The third reason is the ceramic coating is a joke, they will rust fast even with storing the car in the winter and avoiding rain.
My advice is sell them for some kind of money, and buy the
BBK's. I have them on both my Cobras, they burn no oil, still look good, and have great ground clearance.
As far as your X or H pipe, you will have to caught it down and weld flanges on the end to bolt it up to the new headers. I had this done to my 97 Cobra, because the Bassani X-pipe was one for stock headers. I also had to get smaller converters because the converters on the X with shorties are larger than the converters intended for L/T's, and they would not fit right. It looks good, and has decent clearance to the ground. My 96 I have the BBK L/T's with a short BBK H-pipe that is made for L/T's. The 96 has excellent ground clearance, and looks WAY better. I had the exhaust done twice on the 97. I spent way too much on it, so take it from me, go buy a mid pipe made for long tubes. The first exhaust shop did the work and it looked crappy, the second place did it right, and charged three times as much.