Mark ... your mate, Marcello Gandini, is the fellow who created the Khamsin concept, and the rear glass panel was duplicated in his design for a larger V12 powered 2+2 GT that was the Lamborghini Espada ... both cars had a rear window hatch that was virtually horizontal and as such the glass rear panel served a real purpose as a rear view window. A disturbingly ugly aspect that befell Khamsin was what happened when it was adapted to meet post-1975 safety regulations in the USA market, where one-third of production found its way. Those US 'bumper' regulations desecrated many a fine European car, as you'll see here ...