I have the same "issue" and were checking out couple of places. Best would be a non cored section. Didn't find a suitable one on my Lavezzi
2nd best is the area where the original cleats
stern are installed. U shape gives the most strength. Mine is a hardly used 2006 and has stress cracks around the cleat mounting. I would Reinforce the area with additional layers of fibreglass and put a 2nd cleat aft of the original one. You need compression
rings in the thicknesses of the material of the holes so you don't break the fibreglass when tighten down. Then a chainplate as long and wide as the area allows and also connecting both cleats
Section on mine is rounded, so you would need a machine shop that eg mills a 30mm thick and 70mm wide SS bar half round to your shape.