Hi there- you will love this website dedicated to the SJ23 if you haven't seen it yet- look for "SJ 23 tech tips" on google and you'll find the site.
I have had one for about two years and the projects go fast- its a pretty well designed boat.
FWIW- Mine has been using a long threaded stainless bolt with nut on the end to keep the mast in place.
rbensyl, I do know about the SJ23 site - it's great and I'm already planning a number of projects based on their info. Thanks for the message!