Just checked Needlbar and it has the Pritzlaff Rotary listed under National with no reference to Davis at all. The good part - it's a lot easier to find attachments to fit National Rotary machines.
http://needlebar.org/cm/displayimage..._display_media
National made this model (Rotary A) and put a lot of different names on it. The above link has a short bit about the Pritzlaff company that sold machines with that name on them.