Its kind of funny, AHPC/Goodall still builds their boats with slots in each side and it is faster to lace when assembling a boat from bare hulls or re-installing a tramp etc. I don't think the switch is worth it, but has been done before by filling the slot with epoxy+filler (read: heavy) and drilling and tapping the screws. Another way is to get a backing plate in the slot somehow. All a bit too much work for what others still build as the "correct" solution.