I have a centerboard Rhodes 19 that I am very slowly restoring in between my other boat projects. I am replacing the ribs also. For parts and information, Stuart Marine is a good source. D&R Marine also has some parts. Since the O'Day Mariner and The Rhodes 19 share the same hull, keel and centerboard, and rudder, there is some information that is interchangeable. The Mariners that were built from 1963 to mid-1968 have ribs like the Rhodes 19, although the ribs in the cabin are shaped slightly different, from the cabin to stern they are the same. The Mariner Class Assoc. Forum is a good place to get information on replacing the ribs and other work (the Rhodes 19 Assoc. forum is worthless unless you can wait a couple years for a response). The Mariner Class Assoc. site is
http://www.usmariner.org/ , although you have to join the Mariner Class Assoc. to access the forum. It cost $15 per year. It, like the Day Sailer Assoc. forum is very active. It would be your best source for doing work on a Rhodes 19 however. Other than the ribs, the Day Sailer forum has a wealth of information of restoration work.
John