I have an aluminum shelf in the upstairs if my father's barn that I pulled out of my 85 c10 20yrs ago. It is the full length of the bench seat. Has 2 shelves with a lip on them to keep things from falling out. The seat could go all the way back without interference. I doughty it was stock by gm. But is this what you are thinking of? If so, I can get pics for you next time I'm over there. It is simply made, but effective.