I stole the power tools line from
- chris_quilts I sometimes call them power tools with thread, too.
I too am a gear head in love with old machines and that is how I got here. Your BelAir is a Japanese clone. Most likely a clone of a Singer 66, 15 or 99. Their manuals can be used.
if you want a huge challenge, find a locked up Necchi Supernova. Very close tolerances and stuffed full of mechanical wonders. They often lock up if they haven't been used for a while and the old oil hardens.