I own the exact same machine as CD, though not quite in such good shape. It was free and is missing part of its tension assembly. I also have the manual and if you need a copy, I can scan and upload if you'd like.
This machine (the 52) takes the flat disc 'E' cams. They are double-sided, so two designs per cam and they were made in two colors, mint green and red. Color does not matter. The machine will only do straight stitch until you add the zig-zag cam, so it is essentially a straight stitch machine with a cam assembly instead of a cam stack or built-in zig-zag. I really like this stitch architecture.
The 1703 takes the 'C' or Top Hat cams, so the cams for these machines aren't interchangeable. The 1703 was one of the more higher-end machines in its day. Worth fixing and I guarantee that you can fix it yourself.