463 does NOT fit that well into the rotation. When they had engine trouble with a couple of locomotives they had to do a lot of swapping at Osier to put her back into Antonito so she could pull the train. This was early in the season with less ridership. They don't need another one with (even if it's a bit less) a handicap. Any K-28 they received would have been worn out and needing work. A K-37 makes more logical sense from a "living museum" standpoint and a operational standpoint.
They DO need more K-36/K-37 locomotives in service. This would take the pressure off to push a rebuild out before the season started. Overtime it wouldn't really cost anymore than having 5 locomotives in service because the additional boiler time and time between running gear would require the same amount of money for six as it did five. Just general maintenance costs would increase. At least that's my calculations from information taken from a good source.