Here is a link that shows you how to figure out what shank size your machine is (and would allow you to figure out what shank the feet in the box are):
http://www.clotilde.com/pages/which_foot.html
There are a couple of links to charts listing shank size/type by brand and model.
Another thing you can do is take a foot from your Singer with you to the thrift shop and compare its shank to the shanks in the box.