This is what I'm currently using for taking my long-reads to my Kindle. Except it doesn't always work well. For eg, with the recent NYTimes article on the Arab world[0], it didn't give me the entire content. As a hack, I found that selecting all of the content and then using that as input worked, but I'm still losing out on all the images and some formatting.

[0]: http://www.nytimes.com/interactive/2016/08/11/magazine/isis-...

Have you tried adding to pocket and then using something like https://p2k.co/ or https://help.getpocket.com/article/911-how-to-configure-cali... to sync to Kindle?