Tom,
I will second all the advice you have gotten here so far. Been there done that. Absorb and apply the advice offered here as it best fits your time and money and you will come away with an unforgettable experience. Before you leave Chama, stop in at the Trackside Emporium on Terrace Ave and pick up one or more of Greg Scholl's videos, or any of the others that Bob offers, to take home. They are professionally done with views that most of us do not have the time or resources to get. Later you can watch them and dream of when you can return again.
You will find the folks at both railroads friendly and knowledgeable. Enjoy your visit.
As far as what C&TS engine(s) will be available, three of the K-36's are in service, the 484, 487 and 488. Which one will head your train will depend on many variables and you won't really know until they back down to your train in the morning and hook-up. You just might be lucky enough to have a double header. Double headers are awesome.
Let us know how your visit turned out when you get back.