Sorry for the delayed reply, but was enjoying a little sojourn to NG country earlier this week and rode the western half of the C&TS. A little weird riding in a coach with 4 other people total but the ride was as good as ever.
After reviewing the new photos and the book some more, I feel pretty confident you have 5538. I neglected earlier to consider the fact that this is a double deck car, which rules 5645 out, and since there doesn't appear to be any sign of the style 6 lettering, which necessitated a new side board for the D&RGW and number below the longitudinal boards on the car, only 5538 from that collection fits the bill.
There does happen to be a photo of it in Taking Stock but I'm having a bit of a hard time finding specific identifying marks that would provide additional confirmation. In that photo, taken in 1986, there appears to be some graffiti on the wide board on the right hand side of one of the sides that might say "BAB" and then slightly smaller "3ST". That B started about midway between the door and end of the car, so if there's any trace of 35 year old graffiti matching that might be one more clue. Sadly, many of the stock cars are unmarked inside - of the 5 I found in the San Luis Valley, one was unmarked anywhere near Manessa (likely has fallen apart by now - was in really bad shape 15 years ago) and one of the two cars I previously owned only had an exterior number on it that I could ever find.
In any case, I hope that's helpful and glad to see it already has a new roof on it.