I stand corrected. Spray rails start 4” aft the stem and 4” ahead the stern. I had said 5 “ in a earlier post
Actually .... you spotted a weak point in the plans. In looking at the stem dimensions (with side panels on), you'd have to start the spray rail a lot closer to the bow than I specified. I need to correct this in the plans. OTOH, if you want to start 4 or 5 inches back from the stem (for aesthetic reasons), just put a block of wood or a second layer of ply on the inside of the hull where the screw goes and use a screw short enough to stay inside wood. The possible downsides are that the interior block of wood may conflict with the bunk installation (easy enough to work around) and/or may complicate lining the inside of the hull with adhesive-back carpet like material ... some people do that to avoid condensation on the inside of the hull while sleeping and it adds insulation to the boat.
Looks like about 2" or so:
PS: A screw is just one option, and it's an optional option. The curves on the f'w'd third of a GA are not extreme, so perhaps the previously discussed risks are very low. Besides skipping the f'w'd screw entirely, you could provide some additional backup/strength by adding layer of glass over the forward end of the spray rail - you'd have to fair-in the glass edges.