I've been thinking about this for a couple days, and Mike brings up a point that I had forgot about, in that steam locomotives tend to create "dirtier" air (oil, water and general gunk in the air) that modern air valves with diaphragms and "O" rings don't care for. If I remember GCRY added extra driers and air filters to cut the contaminates down.
I see no reason 26 air could not be made to fit in the cab. It does take up more room, but I think it would fit. I see no reason why 26 won't work with K triples as WABCO designed all this stuff to work together.
Operationally, it could be used in the same manner as 6ET in the short cycle mode with retainers. The big difference being when light (5 lb or less) applications are made. The "minimum reduction" on a 26 valve is about 7 lbs. Until you got used to it, you might bounce folks around.
The main feature of 26 air is the pressure maintaining feature. You make a 10 lb set, and ride it for as long as you want. The valve compensates for leakage in the brake pipe and "maintains" the pressure in the brake pipe.
In modern train handling with long trains, air and dynamic brakes and power are used together. As you come over the top of a hill, and throttle back to idle, you put the locomotives into dynamic brake and gather the slack in slowly. As more train comes over the top, you add more dynamics until you have full dynamics applied. If this is not enough, put a minimum automatic set into them. If you need to, add a bit more automatic until the train gets balanced and holds its speed. You then control the speed with the dynamics with a bit of automatic air for help. If you come to a sag in the grade, you have to use your judgement whether to kick the automatic air off, cut the dynamics back to zero, or start pulling with the throttle. This depends greatly on the hill, curves, speed, etc.
To apply this to Cumbres would take a great deal of experimentation. Simply taking a 10 lb set at the top and riding home won't work. The curves will slow you, and sags will slow you, the train will get away on the steep spots and straightaways. The only way I could see doing it would be to make a set that would hold the train back on the steepest spots, and pull the tran through the sags. Which will play havoc on the fire and really piss off the fireman, who is enjoying the ride from the left seatbox. With diesels no one cares if you pull on the train when going down grade. This is common practice if you don't have dynamics. Take a set to hold on the steepest spots and pull it through the sags and curves. I'm sure the engineer would have to use a bit of carefully applied engine brake to keep the train down on occasions.
Another thing which effects this is the speed of the train. The slower you go, the more friction the shoes have on the wheels. At higher speeds (above 20 or so) the smaller changes in grade and curvature have less effect on how the train brakes down grade. The slower speeds encountered on the C&TS would make this a greater challenge.
Would all this work on Cumbres? Yes, but it would require a totally different method of running. Would it be safe? Yes, it could be made so. Would it be cheaper? No, I don't think so. You'd have to keep a hotter fire going downhill, burning more fuel. There would be more wear on the running gear because you'd pull more. And the $64,000 question: Would I do it? Not On Your Life.
It ain't broke, so don't try to fix it.
Let me temper all this with, I'm a narrow guage hillbilly hoghead too. I've had ZERO formal big time railroad train handling instruction. I've drawn on experience and logic to fake my way thru this with satisfactory results. It's a good thing my conductor on the Wisconsin & Southern didn't know what was going through my mind the first night I bravely headed into the dark with 135 loaded hopper cars. (..we have HOW MANY CARS...
... holy #%&..." We did make it though and I managed to stop the whole works on a 1.25% downgrade within 10 feet of where I was aiming for.
OK all you diesel guys out there, I'm ducking, let me have it.
