I Think I can export the existing Red Ranger content as markdown.
I think I can then use the import to reconstruct the blog in WordPress.
The Jetpack plugin and the settings changes don’t work well. See Help! My Markdown Won’t Work in Jetpack for a solution. I gave up too soon.
There’s a separate JP Markdown plugin that works much better, AFAIK. Perhaps I’m missing something with the entire JetPack toolkit.