The 600 and 603 are good all metal machines. They are closely related to the Singer 401 and Singer 500. The biggest problem
is the bobbin winder. Get a manual and follow all the directions perfectly. Also use new bobbins or bobbins in perfect condition. I have one that is a very nice machine. Mine will make a chain stitch, too. The stitch selectors are just like a Singer 401 and will be all gummy when you get it. Worth $20 - you bet. Here is a link about how someone finally got their stitch selectors to work:
http://www.quiltingboard.com/vintage...e-t216956.html
Mitch's mom - it is good to know about the white line bobbins! Thank you!