You can fix the deck lip, install the newer one-piece gudgeons offset from the old holes (drill/tap for machine screws) and be good to go.
Is there an upgrade kit with instruction? Or do I buy a standard later model gudgeon from Hobie and just wing it? The boat has two sets of rudder/tiller castings. One set appears to be the adjustable type with set screw in the tiller arm. I assume both types mount the same with the newer gudgeons??
