I too have a Graybar, actually in a pitiful state. On the case front, in small letters, it states Model 1. It is a 3/4 size machine. Graybar Electric Co had it made for them, with the Graybar name. As stated, manufactured by National, but it is not listed on the Badged Names list at Needlebar or in the Law book. I believe the model is an "Expert BT" Vibrating Shuttle type. I might guess the machine was made in the 1930's-1940's.
The bottom of my case falling apart, no manual, no shuttle or bobbin, not even a single foot. I broke the needle that was in it. I just could not resist it though! Decals decent, Spoked handwheel and slide plates shiny. It is so cute!
I have not researched further since I want to treadle it once I build my universal top. I would love to handcrank, but looks like it would require one with a long curved arm, scooping up. The holes are on what some would call the motor boss, which lies horizontally and is integral to the bobbin winder. The actual motor on this machine is attached to the back.
Would be interested if anyone has any further details.