Sometimes there is an actual threading drawing inside the area that opens near the light, have no idea if this machine does or not, but maybe take a look?
Did you google it? This site has one for sale as well, maybe they have a manual they'd be interested in sharing?
http://www.classifiedads.com/househo...-ad1691162.htm
That machine isn't listed here, but maybe some of these diagrams might help?
http://www.sewusa.com/Sewing_Machine...g_Diagrams.htm