The crossover pipes equalize the pressure downstream, letting each exhaust pulse use both mufflers. There's a HP & Torque gain, but mainly at the top where you'll very seldom see it on a cruiser. They change your exhaust sound some, the H adding lows and the X adding highs. I thought about an H pipe on the '32, but only for about 5 minutes....
Here's an old Hot Rod article that gives you more info than you'll want - https://www.motortrend.com/how-to/x-...for-your-ride/