My 1974 Elna couldn't care less. Anything I can force under the presser foot, she'll sew. My 1952 Singer 301 arrived with four thicknesses of med-light weight leather under the presser foot. I personally would not use that machine for sewing leather. Any vintage all steel machine should be able to handle it. I'm sure my 1940 something Necchi would be fine, too.
Try a vintage treadle - there's no motor to worry about.