We have a set of mid spring cleats on our S31 which we put on a couple of years ago. We managed to source a set that we could bolt on to the toe rails. Avoiding drilling holes in the deck.
You can also get cleats which you slip onto the genoa track - Barton and Plastimo do them I think. Bit expensive if I remember but avoids drilling holes in the deck.
Have them on ours. Bolted to toerail on the inside. Came mounted by Moody with the boat at delivery.
Access from below ? I can check next weekend, if you're still interested (Believe they are directly bolted through, but there is the panel construction to cover.