0503 is the only HISTORIC, operable caboose. Actually, I'm not sure it is operable right at the present time. But the point is, 0503 was the only caboose that the C&TS got from the Rio Grande in 1970. Caboose 0579 is also an original Rio Grande caboose, but it was originally donated to the city of Antonito, in 1951 I believe. It was on display, and was used in various capacities. It was eventually donated to the railroad, and has been undergoing a restoration by the Friends for the past several years.
Caboose 0306 was a conversion from box car 3060. As far as I know it is operable, and is available for charter, but the interior is nothing like an authentic caboose, unless you count the cupola. Caboose 05635 was converted from a stock car, and I believe plans are to re-side it to give it a more conventional look.