Here's a list of 10 unsolved cipher texts throughout history, #2 is the Beale Papers covered in the chapter, #8 is Kryptos (the background of our website). Some date back as far as 1400 BC and some are more recent like the Zodiac Killer.
Here's the paper that Robert Ward of Maryland shared with me via email last year. The stats look solid to me, although I didn't check his p-values. Let me know if you work this into any of your projects this fall!