Yup; I upgraded exhaust system in an El Camino big block 72 SS. Went to header flange size back through the mufflers (3") with an H crossover-there wasn’t room for the X crossover. I have had X and H crossovers in various other muscle cars and the X flows a little better and sounds different. The H works the best at the 18" header extension area. The upgrade made the Elky more frisky, but haven’t done the chassis dyno to quantify the difference yet.