K-28's at least were around until the end of DRGW freight operations. Indeed in May 1968 two K-28's worked a freight from Alamosa to Durango. Previous to that they had regularly worked to and from Alamosa for shopping.
As late as 1961 the Special Instruction still listed the K-27's not only with regard to the bridges, but also had tonnage ratings for K-27's from Carbon Junction to Silverton. Why Carbon Junction? However I notice that the October 1, 1965 Special Instruction no longer had the "list" and doubleheading of any engines was prohibited over both bridges.
Which leads to an obvious question. When was the last time the DRGW doubleheaded up Cumbres. In the 50's three engine trains were doubleheaded (with the third engine cut in), but by the 60's the helper stationed at Chama was gone so I am only aware of two engine trains going up the hill, and they had the second engine cut in ahead of the caboose. I'm going to guess the last doubleheader up the hill might well have been an eastbound passenger special sometime in the 60's.
JBWX