I have glued three bits of 6 mm ply together, with fibreglass fabric between the laminations. The gaff will be epoxied into the long square slot (1″ wide). There will be a through-bolted double eye bolt/nut combo at the marked spot for the sail’s throat and the throat halyard. Additionally there will a couple of holes in the ends of the jaws for a parrel-line.
The inside of the jaws will be lined with leather to protect the mast. The area of the mast where the gaff will normally sit will get a layer of fibreglass for further protection of the mast against dings and chafe.