Hi John:
I'll back up the Art on the31-15/20 idea. This is an industrial machine, with metal gears and body. It was the backup in WII to it's bigger brother, the 111W155. I have both and use them a lot. They both will be sewing long after I'm gone. The Navy Marines, Army all used them. Could our military be wrong? Don't answer that. LOL! Back then it was strength they wanted.
I paid ~ $100 for the head to the 31-15, and about $375 for the head, table and good clutch for the 111w155. Am NOT INTERESTED in selling either one.
Kevin
PS: I also have a cowboy 4500, new they are ~$2600+, Landis 12L, saw one sell recently ~$4,000+ and a seven inch Seiko Post Machine, new advertised for ~$2,800+. Still will not sell my first, the Singers.