Hi Chrisbede,
No the centreboard and mast base wont be compatible with the old
WINDSURFER One Design. Back in the days of old if spares used to be made from wood. The centreboard in that board just drops in and has a strap on top to lift it out..believe it or not the way to sail with the centreboard up(downwind) was to wear the centreboard in the crook of your elbow(a bit like an old lady's hand bag!). The mast base was made out of a piece of wood...the original product was black plastic. You could use a block of nylon or similar.
Those boards are quite sought after and yours looks in good condition so I would look after it! Ok to SUP on if you don't have anything else!!
Cheers!