Luke,
I have a artisan servo motor on a31-15, singer 111w 155. The motor runs very quite, 1/2 hp, low /hi range button, speed knob, and a motor directional switch, it came with a small pully sheave, no speed reducer necessay. it has plenty of starting torque, very easy to controll. bolt pattern was the same as the clutch motor so it was an easy change over.
Steve