exhaust question

[cgoodwin]

My current exhaust has long tub headers to flowmasters then out the back. It's a new and clean set up that came on the truck. I don't have a cross over H or X pipe configuration on the exhaust. I know there's horsepower there if I put one on. Can I just use the same size exhaust piping and weld in my own H pipe configuration? Do I need to do this at a certain distance from the headers? Or do you think this is just a crazy idea?