In 1920, I believe the K-27s (Class 125?) were all still saturated steam with slide valves and Stephenson valve gear. (I would LOVE to see some film of a Mudhen working in this configuration!)
I do recall reading somewhere here of a T-12 being used to help shove a rotary (I don't know which one). I believe it was in the later 1920s or 1930s. I assume they were short of power during a severe winter and threw everything they had available at it.
It would be very interesting to see the K-27 paired with a working OY. Given the timing of OY's arrival on the railroad relative to where it was used and the arrival of the K-36 & K-37 classes, was OY ever used with a K27 or K28?
Dave