The JeepSpeed guys like those frame stiffeners, so they must work. I would have never come up with that design, but it does tie the front and rear suspension mounts together with a length of tubing that has to twist......something that tube doesn't do very well. It also adds strength to the suspension mounts, which has to be a good thing, and boxes the frame more by adding some additional structure.
I've learned the hard way that we need to add some steel to the bottom of the frame rails, before they get caved in by rocks. A simple piece of steel strap welded along the bottom, or a big piece of angle iron, will do the trick. I wonder how much the angle iron will add to the stiffness, unless it's very thick and wide....and heavy. Normally something made of tubing will provide more resistance to flexing, either square or round.
I made frame stiffeners out of 1x3 boxed tubing, spaced out from the frame by a short length of the 1x3 at each end. The seat bolts where in the way of mounting it flush to the frame, and it didn't fit very well with the slight curve in the frame and floor pan. By spacing it out, it cleared the bolts and fit nicely to the shape. Plus, the one inch gap adds more boxing to the frame and makes it stiffer than if the 1x3 was mounted flush along the side of the frame.
Of course, the cage helped stiffen things up also, but I think the frame stiffeners helped as much as the cage. You know how you can wrap your hand around the top of your door and the roof, and feel how much the door moves relative to the roof when driving on a trail or rough road? Now, mine doesn't move....AT ALL!
