Here are the centerboard theories that I mentioned, none will be exact, but may give you ideas. I also added info on the Javelin CB.
On the 1970-73 O'DAY 15 it appears that there were 2 lines for the CB, one pulled CB up, one pulled it down, but the pics that I have don't quite tell the story enough to be sure how it all works. As I say, for the DS II, Widgeon and Javelin..... I can figure it out.