I bought my 1st treadle machine recently! Another member of this forum suggested needlebar.org and there is treadleon.net - these sites have tons of information about antique machines. I hope you can find a link to a manual thru those sites.
My machine is a National, also. Mine is late 1800's - early 1900's. It has a vibrating shuttle - I hadn't seen one of those before - the shuttle looks like a bullet. I am in the process of cleaning and oiling the machine - it is running smoothly, but the stitch regulator is stuck - stuck on the longest stitch, of course. I can't wait to use it - I want to make at least one quilt with this machine ---- I really hope to use it a lot.
My machine did come with 2 belts, a bunch of needles, a box of attachments, and the manual - I got a another booklet that has drawings of the attachments and describes what they do. My manual also has a list of all the machine parts and what they cost.
I'm so excited for you! Enjoy your Birthday present! :D