What I would do is use two 1/4" Aluminum plates for the rudder head and use nylon bushings for the bolts to hold it together. You could have a Teak block in front of the head for a stopping point for the rudder blade, and a Teak block in back.
For the rudder blade you can use wood or make up one out of Fiberglas.
A friend of mine built a rudder head similar to what I've described.