I've been looking at the Kenmore machines, found the insert and adapter. While the seller has a list of machines they know it will fit, they don't list either of the two listed on this thread that will chain stitch.
There is a nice 158-17200 for sale about 200 miles away, so I emailed the seller to see if it would chainstitch. I'll be heading that way in about a week anyway. It has the ability to take cams, and I want that also.