I was just looking at the 1930 proposed design for the RGS 2-8-8-2. It has drivers of 40", axle spacing same as the D&RGW K-27s, Front and rear trucks of 28" diameter, and 54,000 #s of tractive effort. This looks like an articulated (simple not Mallet) pair of K-27s.
Darned if I know how to classify it except as an M-54?
The 1927 proposed 2-8-8-2 for D&RGW appears to use 49" drivers and is a simple locomotive just like the RGS. Its classification would probably be an M-75.
The 2-8-8-2 made from two class 113 locomotives (class C-28?) appears to not any existing narrow gauge mike. The drivers seem to be either 40" or 47". The copy I have is too blurred to see the numbers clearly. It may be a 40" center and 47" or 41" to the tire. This appears to have 53,400#s of tractive effort.
Interesting but useless information.
Doug vV