When I was there in 2014 they were down to just two Trains a day (Mid-September). 480 pulled the first train (Which we rode 1 day), and 481 pulled the second one. It was the same 3 days in a row. 480 has a dog house and 481 doesn't. 480 seemed to crop up in many of my better shots over the years. I wonder if there is a way to contact someone to find out the power scheduled for a day or two, but then I suppose its kind of bothersome for the staff to mess with that.
Hopefully you will see a K-28. Maybe you need to spend 2-3 days to be safe, or once you get there inquire about the following day/s.
Cheers,
Greg Scholl