The Chinese C2 locos and the Russian PT-4 design they are based on are facinating engines. The PT-4 were a replacement for the lightweight 0-6-0 86/Kolomna class which was a Russian military loco. Most all of these are 30 "inch*" gauge engines, excluding the oddball 600cm gauge loco.
Many of the PT-4s were actually built outside of the USSR as reparations/East bloc. Builders included a consortium of three companies in Finland, Skoda in CZ, MAVAG in Hungary, Fablok in Poland and a order with the North British Locomotive Company of Glasgow, Scotland that was killed due to not being able to secure a line of credit for the the order (over one thousand) and the turn Russia was taking by the late 1940s.
Some of the PT-4s that were built in and outside of Russia ended up in China. They used this design for the basis of the C2, along with the similar but larger Polish Px48 design used by a few East Bloc countries, which also saw examples sent to China, for the C4. The Px48s were reportedly diverted from Jugoslavia to China when Tito fell out of favor with Mother Russia and Davenport/Porter filled their needs.
I think it is funny that in the narrow gauge modelling world (Especially On30) we see models of single to small (5-20 in total number) classes of locomotives, but we have yet to see anything commercial from the C2/4, PT-4 or Px48 design, when the combination of these classes are estimated to be over 6000 in number!
I remember Zubi mentioning at one time that he was going to comission a Px48 from someone, but I have not heard anything more.
* "inch" as remember that there was not a true standard inch until the late 1950s, so 30 "inch" gauge range from 750mm to 785mm depending on the country