I found by going to http://reader.feedshow.com/goodies/opml/OPMLBuilder-create-opml-from-rss-list.php and putting in the old blog URL, and clicking "Only alternate links" button, I could create an OPML XML file I could import with the WP-matic plugin.
All I had to after that was create new categories and move my posts into those, re-insert the images into posts, and that was pretty much it! :)