Looks like it will be a diff protector:) It's not lower than the diff so it shouldn't hang up too bad.
I wouldn't have thought it would make anything stiffer, it's the same torsional stiffness which ever way up it is.
should be sweet mate. One thing to worry about might be off road. At hard articulation and the diff comes up under compression, the bar will twist down and could grab the ground if theres something there to grab, like a root or something. That I can imagine would rip the bushings and links clean off the truck.
Might pay to throw shit loads of weight in the back to load it down as much as you can, and see how much the bar bends down. It might not bend down at all.