I was planning to just clean it up a bit. I hit it with some POR-15 Metal Ready I had on hand, which claims to remove rust. Then I thought why not try the POR-15 as japanning? It looks similar and is tough as nails. After a good cleaning and rinsing with water, I dried it and used a brass wire wheel to clean the sides and sole. I then applied wax anywhere I didn't want paint to adhere. I then proceeded to paint the plane, myself, my shirt, the table, and everything in a 3' radius of the table. I'm not sure what happened; it was all a blur.
Looks almost new now (click image for larger view). See lots more photos and comments in the forum.