BoxCar Tom's photos are consistent with my post in #6 above and the four standard coupes that I have owned over the years. One rubber bumper per side on the inner lower back panel and one half round wedge attached with a slotted head screw on the inside of the quarter panel. Note the paint scrapped away on the wedge revealing its material's light color, namely aluminum (or zinc). If your car had a rumble seat, those wedges would be installed in the upper corners of the opening of the rumble compartment (although usually of a different, semi-rectangular shape).
As mercguy notes, deluxe coupes without rumble seats have the same arrangement, as do standard roadsters without rumble seats.