I found a pair of Tacoma seats off CL for free in perfect condition, made my own mounts and used a universal rail for forward and rear movement. This cost me less $100.
People never seem to believe me, but I swear by first generation Matrix seats. I've owned my Matrix 11 1/2 years now (since new), have driven hundreds of cars in the course of my jobs, and I've only sat in maybe one or two more comfortable seats...
Got a photo of orientation? I would think that installation from the front side would be better as there is a nice taper. Dual lip with the flat side facing the front so it can be tapped in from the front. That is how one was installed on a spare...
That little bump exists on my original panels. I copied them exactly, and that bump is there. It looks deliberate, but I'm not sure of the function. I also have a set of panels from another truck and same thing, the bump is there. If you don't...