I think he wanted to see how much clearance he had to route the pipes but I am thinking with the roll pan maybe going out to the sides, yet there still is a fair amount of rear clearance since the back end is stock height to exit under roll pan, I have a few weeks to figure it out!
Roger don't worry that won't be an option. There are a few steel crossmembers he can attach to on the bed subframe. I think it was more for clearance referance than anything else, also he's worried about room, I guess Flowmaster Delta 50's are some big beasts of mufflers, around 20" long?