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It''s hard to say without knowing more about your boat. Talking to the former owner(s) would be best, but it may also be something you can solve by using SailNet''s e-mail lists and archives, which address a very large number of different boats.
If you have a full keel, I can''t imagine why a centerboard would be necessary, unless it is a shallow keel and the centerboard can be lowered in deeper water to provide additional stability and tracking to windward, helping to prevent sliding to leeward.
There is a model of the Catalina, for example, which has a swing keel--a centerboard which can be pulled up to nest inside a shallow keel to make trailering easier.