I think the Santa Fe 2900 class are one of the most famous heavyweights, the unavailability of light weight metals during the war being the official explanation. But I believe they had the reputation as the best steamers of the Santa Fe 4-8-4's.

The Rio Grande never bought any narrow gauge articulateds even tho they had 2-8-8-2's and 4-6-6-4's on the standard gauge. They liked outside frame just like the East Broad Top and the White Pass preferred inside frame. Clearances may have been an issue. And in the case of the Rio Grande there were limitations like the Lobato trestle.

The NdeM articulateds look impressive by themselves alone but I think I remember a shot where there was someone standing next and the locomotive looked diminutive for an articulated. A K-37 is a reasonably big locomotive for narrow gauge, but I think the Rio Grande would have asked for something like an articulated K-36 and that would have just been too big.

I have always suspected that the NdeM in the 20's wanted something that looked cool and contemporary and they got sold on the 360's by their modern look. I am not sure they were that good a fit and the Puebla line rail, their last resort, was too light. Really a shame nobody wanted them and they went to scrap so soon. Kinda like the NYC Niagaras with their high carbon boilers and Pennsy T-1's that slipped too much. You have to wonder why the Pennsylvania RR did not try Giesl on the T-1's as they had smoke problems too apparently. The engineers got smoke right in the face, I believe. I had a relative in Altona, retired from the rr, who told me in 1959 they were not liked. The K-4's were the engineers' favorites.

I digress.