There are a few Kenmore folks here that will give you better/more info the specific machines you're looking at.
I would suggest checking your local craigslist for machines. I cruise local areas all the time simply using the search word 'sewing' and get tons of results. Just about any all-metal, vintage machine will probably be good for your purposes. Easy to maintain. You can also check out Victoriansweatshop.com. Lots of good info there and perhaps a few more Kenmore folks - not sure.