It’s still a work in progress, but here’s the beginning of my Tumblr importer:
The basic idea is that it takes the responses from the API (which are JSON) and converts them to TOML. The included theme is designed to look at the TOML and figure out what kind of post it is (link post, audio post, video post, etc.) and create the appropriate wrapper for it. Obviously, to use it yourself, you’ll want to add CSS etc.
My blog is the basis for this tool and it worked pretty well for me there: https://blog.carlmjohnson.net.
My plan is to do some more work to make it download images for permanent reference when I have time for it, but other pull requests would be welcome too.