These are not industrial sewing machines and can't handle heavy leather. You might want to read about Singer 201-1 (Treadle Operated), 201-3 (BR external motor with belt drive) or 201-4 (hand cranked), or the K versions made in the UK between 1935-1962. 201-k, 201K3, 201K4, 201K21,23&24. . Germany also made a verson from 1935-1944? 201D (cast iron model as 201K3 etc.) There are forums regarding the Singer 201s and I think there may be a Facebook group of users. I think all of these models could use a servo motor in place of its current motor if needed. Here is a link to Harry Rodgers on youtube discussing it. Harry is a Leatherworker, if you haven't heard of him. Best Budget Leather Sewing Machine? - Bing video.
Any Singer 201 with -2 (I believe) has a potted motor which is attached directly to the machine and doesn't use an external belt. Most require checking out the wiring in the motor.