I forgot an important dimension the vertical distance from the rear bottom planning surface to the outside (rearward) top corner edge of the transom motor board. At 8'- 8" that is a small boat and with a 50" afterplane that is a short boat. At 80 lbs that seems to light for plank construction, would you weigh it and what is your weight (if you don't mind?). Then can get into engines.

When you get to working on the bottom run a 3 or 4 ft straight edge long ways from the rear bottom edge forward at several cross ways ward forward locations and cross ways at the rear planning area at several forward locations. Need to see how flat the rear planning area is for the last 3 to 4 ft.

The rear sponson rat nibbles and other small dents gouges etc can be filled with thickened epoxy ( I use cabosil as the thickner). The deck holes need a ducthman wood patch to preserve the original deck contour. These planked bottom racers were typically clear varnished on the bottom and sides since they required regular attention to keep the bottom flat and varnish was a quick sealer. I would not epoxy coat the bottom with the planks that move somewhat and the epoxy will crack at the seams that look like they are caulked.