The diamond shaped piece at the rear window is a filler extension to complete the rear window plug, as can be plainly seen on the car pictured by Tony. This is the biggest telltale sign of a Superbird, as the rear window was made smaller to accomodate the wing/trunklid configuration. You can clearly see the plug, which was very hastily tacked in and then hurriedly covered by the vinyl top. Most times you will find maybe as little as 4 tack welds holding in the plug, and absolutely no body filler to transition the plug to the body. Very shoddy craftsmanship to get the cars out!! Geof