There are only 3 C-16s, 223 (Salt Lake City), 268 (Gunnison) and 278 (Cimmaron).
RGS 42 was originally D&RG 420 - a C-17.
As I recall, D&SNG started work on restoring her but later decided that her low tractive effort and therefore her smaller train size would not be economically reasonable.
As I recall, the D&S got 486 instead and rebuilt her. It seems that I read here that the cost to rebuilt 42 was about the same or more than a K-36.
The Durango group restoring 315 (sorry I can't recall then group's name) has, as I recall, the D&S's occasional help to get her road worthy but the restoration funds are not comming from the D&S. It will probbably be run on the D&S.
315 is C-18 and was originally F&CC 3 "Elkton".
If I've made any errors in recallection, please feel free to post corrections or amplifications.
Doug vV