Not suggesting you add an X or H pipe but thought I would mention this.
As with anything there is an ideal placement for the X/H pipe, ideally you would attach it at the hottest point of the pipe(s). Whats happening is the heat differences from one pipe as opposed to the other, causes a pressure drop, which in effect sucks the exhaust out of the oppossing side and vice versa. (ever crack a window/door in your house with the a/c on and the outside temp being extremely hot? simillar effect)
If you cannot measure the temperature of the pipe, you can put a strip of paint on the pipe(s), keep checking it, the point that burns off first indicates the hottest point and a good place to put the X/H pipe.
I just placed mine were it was the easiest to get too, my intent was to knock the buzz out of my six's exhaust tone, the improved performance was a happy suprise.
In all honesty, if I hadn't already ran the duals, looking back and knowing what I know now, I woulda went with a single 3" to a single in/dual out muffler.
If your looking for that screaming six glasspack rasp, do not install a crossover pipe and definitly go duals.
Do you have any pictures of your truck, sounds like an interesting project, good deal on the engine as well?
