I did it in a couple of hours. I cut a new inspection port. Removed the old hardware and wood backers. Drilled 4 holes and installed the new rudder attachment and backing plate, and was finished.
The repair would have been better had I remembered to fill the two screw holes left on the bottom of the boat! But I can assure you that it takes a while for water to seep into the holes when out on the lake, and a sunfish can hold a LOT of water.
All I needed was a saw, drill, some epoxy and a couple of wood shims for the backer plate. Love the new rudder now. It was worth it.
Mike's comments are spot on. I have done 5 or 6 of these upgrades and the job takes under 2 hrs. The main pain is cost.
If you get new parts, the upgrade will cost upwards of $500 or more. I can sell you a nice reconditioned new style rudder assembly and all the other parts you need (external rudder gudgeon, internal back-up plate, stainless steel mounting screws, inspection port, and even a short piece of aluminum trim to fill the gap where the old bronze deck plate was located) at decent prices. You can then sell your old rudder assembly and hardware here on the Forum to help defray the cost of the new rig. E-mail me at: aglos@colgate.edu if you are interested and I can work up a good, off season price for the items you need to do the retrofit.
The new rudder rig is significantly better than the old rig. The rudder blade shape is better upwind and down, and the kick-up mechanism (with the rudder head side springs) is much better than the old rig.