My X is a Dr. Gas....and it is literally about as old as some of the cars on this forum. Dr. Gas was the first company to market an X for the Mustang. Back then when you ordered it, it came in a box about the size of 2 shoe boxes put together, and it was in 11 pieces. You had to fit and weld it together yourself. The X portion is literally two 90 degree bends that are siamesed together in the middle. Then you have some straight pipe sections coming off all 4 corners...this is where you determine how wide the inlet and outlet are going to be (as in wide in the front to meet up with the headers, narrower in the back for the muffler flow tubes). Then you have for 45 degree bends on the ends to finish it up. Then once you have all that how you like it, weld on your ball/flange ends if that's what you're using and you're all set. It really helps if you have another one to use as a guide...my buddy used my Dr. Gas as a guide for his.