The Finescale Railroader 2006 Narrow Gauge Annual has a couple articles of interest. There's a short article on "Sumpter Valley Today", and a 50-some page articles on "Rio Grand Narrow Gauge Cabooses" by Robert Sloan.
This seems to be a significant update to the caboose chapter in Sloan's "A Century + 10 of D&RGW Narrow Gauge Freight Cars". Plus there are lots of pictures, both historic b/w and color of stuff that still exists. Of interest to me is a couple photos of 0579 in the early stages of restoration. Note that they included some things we later redid, so don't go out and mount your steps like is shown.
A friend alerted me on this and I thought I would have to mail order or go to Caboose Hobbies, but the local Hobbytown USA had it. Published by Westlake Publishing Company.