Maggie,
My favorite site is the Needlebar Picture Library:
http://www.needlebar.org/
Eldredge is the main National brand name. Uses R221 bobbin and Eldredge Rotary needle or Boye 21. Well worth $10 if it has a bobbin case and you could probably get it running and sewing well. More would be learned in restoring to good working condition than performing an autopsy.
Jon