Hi Edd, you should be able to sort it from these pics (original 1978 assembly plans for my Optimist- see my harbour,- might pick up the stays from that) which I'm re building. If you want me to PM you, -PM me with email and I can send them to you that way as well (will probably come out larger/ be able to zoom in a bit maybe)
Original had a Graupner winch, but you could substitute a sail servo using the same sheet layout. Sheet tensioner hooked on 'P' is a rubber band. I have replaced the original stays with .020 stainless wire fishing trace (original wound trace rusted and frayed) which will last forever and no holes in fingers.