Even with the damage you got a great deal IMO. Singer used the same black tophat shaped cams in their 400, 500 and 600 series slant needle machines. At some point Singer added the white tophat shaped cams in the 700 series Touch & Sews, the difference being a second set of bumps on the cams to control the feed dog movement for a wider variety of stitches. The white ones won't work in your machine but the black ones will.
Looks like Sew-Classic.com carries a top tension assembly that can be made to work.
http://shop.sew-classic.com/Singer-T...422403-455.htm
Your other choice would be shop around for a vintage one to fit.
Rodney