So I bought an old Ensenada 20 from 1972 on eBay, so cheap that I figured if it's garbage, I can afford the loss. Therefore I didn't even look at it before bidding. Once I got it, it turned out to be reparable. The seller claimed that it was "sailable", but that's a truth with modification: The rudder did not fit.
First task was to replace the rusty keel bolt of uncertain condition. I made a new stainless bushing, 1" OD and 1/2" ID. I also made two nylon bearings, for the 1-1/4" holes in the hull. A design drawing I found on the web (for a Balboa, same keel) turned out not to be true, so I had to redo it based on what it actually looked like. Here is the bolt at it used to look:
Here is the new hardware, all in SS316 and nylon. The will also be rubber gaskets. The drawing in scale 1:1 shows how the keel is mounted, with the nylon bearings shown in green (the clearance is very small).
The old bolt and bushing compared with the new hardware.
Installed, with some 3M 5200 squeezed out:
The hardest part was to get the old bolt out, using a sledge hammer. The rest was easy, but one needs a metal lathe to manufacture the custom hardware (bushing and bearings).