Nice find! I like the way the needle plate and bobbin plate have their markings inlaid with green paint. A lot of the Japanese machines have a presser bar release so you can darn with the SS foot on. You just push down on the top of the presser bar, and it may release with spring-loaded action.
Edit: You would push down on the outer ring to get it to release. Here is a video demonstration at about 7:40:
http://www.youtube.com/watch?v=fFSJSkx9zNM