I'm not 100% sure what it is but I do know its part of the rear end/suspension. Kind of looks like an anti roll setup.
Ding Ding Ding!!!! This isn't a direct fit and will require some mods. After talking to an engineer from the company We have conconcluded I willo have to lengthen the Frame Mounting points by 3/8 each side. The other way around it would be to notch the Frame rails by 3\8 inch each side. They were very helpful.