Okay, that's a start. Have you ever seen a pic of what they look like somewhere? I don't think they can slip under anything, the seat cover hog rings completely around the opening.
Thanks.
The two clips at the top of the seat back boards slip into a pair of little hoops on the sheet metal brace welded on the top seat back frame. The seat back board has a metal re-inforcement along the bottom with a little screw at each end that screws into the bottom of the seat frame.