You could probably mount any standup block on your O'Day and it would work fine. The Beneteau parts website requires you to register, I could look it up if you knew the boat better you saw it on. Is it a First, a Oceanis, or something else? Size would be helpful as well. I think it would be much easier for you to just buy a stand up block and deck mount it or attach one to a stanchion.
Also, the Beneteau parts website is horrible to navigate.