For removal/refitting… Tip the boat on her side, put the centreboard fully down and mark where it sits. When you replace, just line up the marks and the holes should all align. However… if you’re going to sand it down and re-varnish, these marks will be lost, so…
After removing the bolt, and before removing the centreboard, put a long piece of strong thread through all the holes. and tie it in a big loop. Take out the centreboard and pull the thread through. Cut the thread and tape it in place. When you come to refit the centreboard, tie the thread through the bolt hole on the centreboard. It will already be through the bolt holes on the centreboard housing. Then when you guide the centreboard into place, simply keep pulling on the thread and you will end up with all the holes aligned and the thread running free. It’s MUCH easier to drop the bolt in at this stage and avoids any frustrating “Hunt and peck” techniques. 😉