What several sources describe as the first narrow gauge passenger coach built in the United States was a D&RG coach built in 1871 called "Denver." It had a clerestory roof, 2-and-1 seating, and measured 40 feet overall, 35 foot carbody, with a nominal 7 foot width.
I've never seen a photograph of nor a description of a flat-roofed D&RG coach. Therefore I believe the D&RG purchased no such cars.
I believe the second generation of D&RG coaches from the mid 70's also utilized a 2-and-1 seating layout, but with the width increased to around 7 foot 7. I'm not sure, however, as most sources tend to gloss over that period of the Rio Grande in favor of focusing on the early 80's expansion era.