Full Vert body stiffeners needed on a 76'

[Gemp]

I was laying out my exhaust last night and my overwhelming need to get my tailpipes to an side exit position, So Jr and I don't have to suck fumes in the back window. Since I planning a on bagging the rear, I'm thinking of tunneling the frame rails and hanging my mufflers on the outside of the frame rails and exiting right in front of the rear wheels. Now lays my issue....I would like to run an good size muffler...Like the new fully welded ones I have sitting on the shelf. The thing is the vert body stiffeners are in the way. My truck being an 76' half top....Are they really needed?