I would think that conversions such as on the K-27s would require some major work. There was, however a successful conversion "kit" made by Franklin which was used to convert many standard and narrow gauge locomotives to piston valves. Nevada Northern 2-8-0 #93 has this conversion. Some of the Oahu Railways outside frame engines were also converted in a similar manner, perhaps with a home grown conversion or one from a different manufacturer. I don't know if the OR&L used the Franklin unit. -- Ed