Check the hobie catalog for the following and you won't need new castings:
[color:"blue"] EASY RAKER Provides the same
adjustability to the older Hobie 14 and 16
upper and lower rudder castings as on the
later model boats. Simple installation requires
electric drill, drills, and tap. Use your own
drills and tap or buy tool kit that includes all
necessary material except drill motor.[/color]

It's a whole lot cheaper than new castings.