with a little research, you will find that a lot of the vintage machines can be converted to a hand crank. and lots of electric machines can be put into the pretty treadle cabinets. Yahoo group <Vintage Singers> is first rate info.
there is a site devoted to treadles <treadleon>. 15-91 is a heavy-duty (not industrial) machine and is a gem for FM quilting. You can find 99's all over, cheap. they are a 3/4 size machine. Love the Black Beauties ! smitty