Your question interested me, Jim, being a lover o vintage machines, though non-electric I have only a hand-crank. I found this on Treadleon.com: There is one other Singer treadle model that should be mentioned, that is the 201-3 or 201K. The 201 machines were introduced in 1936 and are generally regarded as the best machine Singer ever designed. They are a full rotary, fully geared and ball bearing equipped version of the Class 66 movement. The vast majority are electric, but they are occasionally found in treadles. If you find one, don't pass it up!
The same site was quite complimentary about the 66, and it does reverse if built after World War II, so if you don't find a 201-3, you may enjoy looking for the 66. They were manufactured into the 1960s and millions were made. Modern feet will fit ones with a side-clamping screw, and many pre-1920 models have been refitted with that. I wasn't aware of it. The site says that refit can still be done.
For more information about machines, you might look on Yahoo Groups to see if there is a TOGA organization in your state. I know there are several - Tennessee has one and they get together every year for a weekend of show and tell, clean and learn, and what-have-you. Best of luck in your search for a 201 unicorn! =)
Susan