Just occoured to me. If you are drawing a constant arch around the front of the table the distance from the nail to the front would have to be the same as the distance to the sides. According to my estimated measuremnts that would have to be 32". That must mean that the previously mentioned 24" would be from the front of the chip tray to the front of the table. That might actually be helpful in positioning your tray.

Again please remember my measurements were estimated by looking at the dirt and wear patterns and noting where the rail and tray edges were and where the staples and other creases were. Then I marked these all out on a piece of paper and calculated some assumptions.

Again, good luck hope it turns out good.