I was thinking Singer 15-91 too. You can probably buy one on one of the lists for $100.00 or the last day of an estate sale for $50.00. It drops it's feed dogs. You can't kill it with a stick. It's supposed to be the best for FMQ.
I know nothing about Kenmores. However, you can search google with "Kenmore 158.***" and click on images to get an idea of what you're looking for. Most people don't know what model machine they have, so you'll need to know what you're looking for.
When you're deciding, be sure and pay attention to the size of the harp area.
bkay