Macybaby, I've never seen the chain stitch adapter with the squarish plate...Learn something new every day, huh? I don't think they're as common.
mlmack, The one for the 158.1755 looks like yours EXCEPT for the feed dog slots. Mine has 1 larger rectangular slot....as does my needle plate insert. These 2 adapters are on ebay quite frequently....either in a set of attachments or alone. But most sellers have no idea what they are so they're just listed as Kenmore attachments!
A good way to find out which machines will take which adapters would be to search "Kenmore needle plates" or "Kenmore needle plate inserts" on ebay....there are always a LOT of them on there. The after-market needle plate inserts are still being made. And look at the list they fit. Those machines will all do a chain stitch. You just have to get the chain stitch set with the correct needle plate. It's worth looking for...my machine makes a really nice chain stitch.