Hi,
I recently came across a bit of software AozoraEpub3 which can convert Aozora .txt files into epub3 format files. See the following link for more information
http://blog.preining.info/2013/01/10...nts-to-kindle/
it can produce either vertical and horizontal format files, depending on settings, and can also be set to exclude images. It also seems to handle ruby text when present. As the interface is in Japanese, the above link is useful for explaining how to use it - although as icons are used a lot some functions can be guessed at. Once an epub3 format file is produced, this can be run through kindlegen to produce a version for a Kindle.
Using this I have been able to produce vertical text books for my Kindle White. These also include the ruby text. Pages turn from right to left as expected when going "forward" through the book.
The other bonus of this is that by looking at the contents of the epub file one gains an idea of how to create a vertical text format book - which can be applied to one's own material.