Hello Craig
After looking at the photo posted by Russo, I would build the bents using the standard gauge R&RGW trestle drawing from page 183 of the plan book. I would then use the narrow gauge D&RGW trestle drawing from page 184 for stringers and etc. That is the way it looks to me, but it is your railroad.
Without some objective information from D&RG records, it is a judgment call. Build it, then some chap will come up with an AFE or sumsuch to approve or disprove what you have done.
I have used leather dye on what little bridge work I have done. I have 3 or 4 colors I bought years ago at Tandy Leather. The color does change over the years, but that just adds character.
Rex Beistle
NMRA RMR
Estes Valley Division