Behind the seat speaker panels

[Bullett]

Looking at my newly acquired 62 c10, noticing it only has the kick panel speakers down by the floor pan, no rear speakers. At one time it had some type of rear speakers because the wires are neatly coiled up behind each seat corner. It almost looks like a blank spot on the upper cab corners behind the seat like there might have been speaker panels there also. Do they make speaker panels for this location? Went on ebay but found no such thing. Found plenty of kick panel speakers but nothing for behind the seat.