Knee bar was common here on the ones in domed cases, but for cast iron Singers in general I think pedal gradually became the most common. I'm not sure when it happened. I've seen very early foot controllers too, and my thoughts have been knee lever was for some reason popular early on while pedal sort of took over at some point, both options existed side by side way up into the 50s. How old is your 201? My 201 is a belt driven machine, and I suspect she will be suprised how smooth running it is, compared to even the most modern machine.
Congratulations on your find :- )