There really is not a lot of info on those machines for year. Look at a thread I started called the dark underside. Wealth of info was shared there. That bottom right knob would be for dropping the feed dogs, just a hunch. One direction drops the other raises. A generic manual is about the best I can do. Cari has pretty much moved over to Victorian sweat shop forum but she knows a lot about the dates etc on these machines.
I'm going to post about a mystery machine in a few minutes... It is already up at VSS.