U.P.'s first order of 4-6-6-4s were (I think) originally numbered in the 8000 series, but as time went on they seem to have been either renumbered, or later Challenger orders were give lower numbers. Problem is, nobody in our club models U.P., and other than admitting to some confusion as to why U.P. numbered some locos they way they did, they can't be of any help.
Does anyone have a web reference that can straighten out the question of exactly what the original Challenger road numbers were, and when U.P. changed them, Etc.? So far Google hasn't yielded anything useful, but maybe I'm asking it the wrong questions...
~Pete