Mine is all wood (3/4" marine plywood) but similar to yours . The rudder simply pivots in the frame. I have a Nyloc nut and bolt through the "sandwich" and a couple of coned washers to spread the load. You will need some rubberized washers between the metals. Use some industrial belting or the sides of an old tire for your friction washers. You will need four rubber washers and two metal ones. Then just tighten the nut as necessary to hold the rudder down. I simply reach over the transom and push it down. You may need a handle or something. No biggie!
Seafarer 29 KCB