There's quite a history. The best write up is in either Will White's Sunfish Book or the Sunfish Bible, which has Will's book reprinted as part of it.
You could also sail over to the Sunfish Class Page (the link is on the main page of this forum) and get all sorts of other information from the FAQ.
The First section of the Sunfish Bible, "The Sunfish Book", introduction and first chapter has most of the info you may need. The “SF Bible” is available through the Sunfish Class Page. American Sailboat Hall of Fame, (http://www.sailamerica.com/halloffame/sunfish.cfm), has some other info. There are a couple of charts out on the web giving a chronological history (one is found on the FAQ’s page, by Daniel Feldman (Wind Line Sails) and Al Barsa, Jr.). Yahoo Groups Sunfish Sailor (http://groups.yahoo.com/group/sunfish_sailor/) has some info in the files section including a brief history by Daniel and Al (an expanded chart history). Check the ISCA rules on the SF Class page for diagrams of the old and newer styles of rudders and daggerboards. The newer rudder was introduced about 1971. An even newer (plastic) rudder has been submitted for approval to the Sunfish Class, but not yet approved. Another possible source is Sunfish Manuals (http://sunfishmanuals.com/index.html). As it is a “new source” for me, I have not been able to get a look at the manual. Read the "Tips and Tricks" section on the Class page and the FAQ's for info on restoring your fish. Also check past threads on this forum for more repair info. Don't forget Vanguard (current maker) for more possible info (http://www.teamvanguard.com/boats/m/_general/home.asp)