Looking at my cab floor it appears that there was what I assume was a seat riser removed (front and both sides, but not back) at some time, see pictures attached.
I am not anticipating installing an original bench seat so I don't think it will be too much of a problem but I am guess that at least across the front the riser provided stiffness to the floor panel, regardless of what seats I eventually install should I be planning to fabricate a reinforcement as part of my cab repairs?