I have a 28 special coupe I installed the top wood in. Standard and special coupes are similar, but of course, not quite the same. The piece of wood in your picture is like the curved ones in my kit and I am pretty sure they go between the rear wood over the back window around the curve of top as it goes to the back to the quarter window. I think it is used to tack the upholstery to when you install the curved upholstery covered rear corners. The small pieces were not in the special coupe kit, so I have no idea where they are used on you std coupe. I am attaching a picture of my original special coupe top wood. The area I believe the curve wood goes is in the upper right corner of the picture, which is a little different from a special coupe.
Rusty Nelson
