I've converted two boats into CC's from their original configuration back when I was young and dumb
One was a 23 ArenaCraft and the other was an Alaskan skiff used for Salmon fishing. It was fun but I would never do that again these days. Very expensive and takes twice as long to complete as I expected. The 20fs rides great with a flotation bracket and a nice light motor on the back.
Like Denny said their are tons of 20sf's out there ready for some love.
strick