I agree with Marshall about the rudder connection hardware. It's likely the 'old style' which will function but is not superior in ease of use to the newfangled, spring loaded, kick up rudder attachment hardware. They sell it at APS: APS - Sunfish - Rudder, Tiller and Daggerboard
If it were mine I would worry about the rudder hardware later and take it out for a few sails and see how 'wet' the hull gets after a few hours on the water. I'd prefer to see if I could shore up the hull first so it takes on less or no water before springing for a new style rudder at $$$. You might also be able to find the rudder and hardware second hand somewhere for a lot le$$. One place to look would be the yahoo group SunfishSailor; lots of tips available there on how to fix up and upgrade these fun old, wet boats.
Disclosure: I've sailed Sunfish since about 40 years ago and have worked with a youth sailing program that uses Sunfish for the last 2 or 3 summers. No affiliation with APS.