Between the roof braces "side to side" bracing and I would assume the "rails" running lenghtwise in the roof metal there is alot of structure.
Thought experiment... Imagine a cereal box with both ends open. It flexes side to side right? if you add braces it will effectivly stiffen the box up.
Thats what our jeeps are like, a big cereal box with stiffeners... (no toy inside), once you start cutting them out you are going to get more and more flex. This is where the "Taco" term comes from. This just isnt one of those things you can slap in, Unibodies behave much different than cab on frame vehicles.