That's it, Brad. Thank you.
DADS50, That's the "tray" under the seat that I referred to. In my Suburban, there was a round plug in that hole. The hole in the Suburban's floor, under the driver's seat, is larger and and irregular shape (not a circle).
I think Denny posted a thread on that hole and plug, speculating on the purpose. I think it was mostly there to allow water/moisture to exit the cab? I could postulate the possible air-exit/circulation due to Bernoulli-effect/principle air-movement (a principle that is re-named "road draft" in helping remove un-needed/wanted gases from inside the block/engine).
I have one of the cardboard seat-backs that I bought 15+ years ago from Jim Carter. I bought it before I knew that is was standard-cab/seat-specific and that it was not used in later A-D years. The cardboard seat-back is still in an unopened shipping box.
