M_Boats: M-17 cabin top thickness and halyard winch

I have a deck organizer and line clamp to install on the cabin top of my M-17. Anyone have an estimate of the thickness of the balsa cored cabin top? Another question is about mounting a halyard winch on the cabin top for the main halyard. My 1975 seems to be the rare model that does not have this winch. Any advise on adding the winch? It looks to be the same size as the winches for the jib sheets. Thanks Robbin hull number 056 "My cousin saw a sign that said drink Canada Dry. So he went up there."