I'll do the other side and then determine the final shape or line to cut the outside of the board. It will probably end up being a straight taper - narrow at the front and gradually getting wider toward the rear of the boat. I decided to reinforce the sides at each screw attachment point with another piece of 1/4" plywood. To keep it simple and light, a flycutter was used to cut some 1.5" diameter "washers" from 1/4" plywood. These were epoxied in place on the inside of the boat and held in place with a screw and a temporary duct taped block on the outside of the boat. I am not going to permanently attach these rails until the boat is out of the basement. Hate to add any unaccounted for width.
After a bit a trying different lines, a straight line did not work as it made the forward foot or so look like it bulged out due to the shape of the boat side. So I used a strip of plywood to create a curved line and cut it on the band saw and sanded out the bumps and saw lines it until I had a smooth surface.