The body may be from a standard gauge car. The ICC Bureau of Valuation records show D&RG 0797, 0798, and 0799 as built by the Peninsular Car Co. in 1890. They were 60,000 # capacity wood cars, listed under Account 57 (Work Equipment) as 'Construction Cars.' I would guess outfit cars. A group of cars numbered between 0768 and 0799, all built in 1890 by Peninsular Car. Co. appear in the ICC records, circa 1918. The 1923 D&RGW Official Roster lists Nos. 0790 and 0794 as part of this group still remaining as bunk cars. No. 0799 is not on the roster, suggesting it had become a lineside shed by that time.
So, according to the rosters prepared by the ICC and the D&RGW, this doesn't appear to be a narrow gauge car after all.
Charlie Mutschler