The content from my old blog is coming soon, it is work in progress :-)
If you are interested in the details of the migration, check out the blog code at GitHub, especially blog2md-master/index.js and gatsby-node.js. The core of the process is using
blog2md to turn Wordpress export XML into .json files and then loading those into Gatsby and suing custom code in
gatsby-node.js to create an "adapter" node type
ContentPage for both new Markdown-based posts and the old ones from the .json. In practice it is somewhat more complicated that it sounds - just as always.