Another update. I decided to try wet sanding the top tube to see what's up with the paint, and to what extent there are rust issues. Oddly, the paint went from brown (at left in the photo) to bright yellow, then, as I got through the yellow, I found a layer of white, then bare metal. No purple. I'm not sure what to make of that, but I'm starting to think chemical stripper and black rattle can is the way to go.