[garygibsonsf]

Hey AT - I'll have to admit I did rather struggle to make all this work. Your advice is excellent, unfortunately, although I have some familiarity with things like HTML, I'm a no-brainer when it comes to stuff on this level. I did follow your suggestions as closely as I could, but unfortunately they didn't pan out for me. Thank you, though, for taking the time to help me out.

What did work, however, was converting the cover-less books to Epub format in Calibre, having first included a cover image in the Metadata via Calibre's menu system.

Instead of then converting the Epub back to Mobi in Calibre - which always produces terrible formatting issues - I instead navigated to the newly generated Epub file, and ran it through Kindlegen. This produced a perfectly formatted Mobi book, complete with cover. I'm guessing Kindlegen somehow strips out all the problematic formatting caused by Calibre. It works, anyway, and might be a little easier for people like myself who get a bit list in command-line land.

Just to sum up for anyone else reading it with the same question in mind - add mobi book to Calibre, use Calibre to add a cover image, then use Calibre to convert the mobi to Epub, move that Epub file to Kindlegen, then run Kindlegen, generating new copy of Kindle book with added cover and otherwise identical to original.