Thanks! I pulled it off a couple of days ago. In addition to the machine screw/washer you mentioned, there was a wooden block in the cutout for the top pintle that blocked the rudder from moving up. (I'm fully in support of a "belt & suspenders" approach when it comes to keeping the rudder on!) After that, the only impediment was the 3/16" thick layer of bottom paint all over everything. It came off easily with a little scraping, and as my boomkin is being replaced, I didn't have to worry about scratching it.
PS: I'm semi-blogging about working on the boat.