If it works for the Paperwhite, it almost certainly works for the Kindle 3, 4, and 5. The previewer is just totally broken for those devices. The previewer shows you the old mobi format for all eink devices except the Paperwhite even though all of them except the first and second generation devices should have been upgraded to use the KF8 format.
All of the Kindle eink devices that accept the KF8 format use the a customized webkit browser to render HTML/CSS. As best I can tell, they are pretty much feature compatible. For something like furigana, you will definitely have to test on actual devices.