That is a nice find, it's a Convertible bike that can be used as a boys or a girls bike other than that I don't know much about them and looks like it might clean up.
AMF bought Shelby around 1954, but only used the name through around 1962. This bike is probably toward that later end, though they continued to make the sister model, the amf Convertible, through the 70s.
-Adam