Beaniekins,
compare your machine with these 27s I found on Ebay:
http://cgi.ebay.com/ANTIQUE-SINGER-S...item3364ef35a2
http://cgi.ebay.com/SINGER-TREADLE-S...item27b88a9dea
Some of the older ones were fiddlebase...
I just noticed that yours has the spoked handwheel, which probably means it was not electric, originally. Spoked handwheels came on machines that were either treadled or hand cranked. Many were converted to electric machines later. Your machine will have the bullet shaped shuttle below those two slide plates on the base. It winds a long bobbin, rather than the little round ones that modern machines use. The TreadleLady has some good videos on how to wind those bobbins and thread the machine:
http://www.youtube.com/watch?v=TFQ6fTVnkT0