How strange you should mention these, they are not at all like the cars discussed here
http://c-sng-discussion-forum.41377.n7.nabble.com/Coke-Cars-and-Racks-td7914.htmlI would hazard a guess that these were quickly converted Flatcars for said service, keeping in mind that both roads were under-equipped and over whelmed with traffic all for Leadville. And I'd suspect these were of the D&RG, I say that since the Grande had the greater traffic base but of that I'm not certain.
I also thought it was rather funny that the 3 commonly available pictures taken on that day don't show those cars, having not been yet placed or just moved before the time of picture taking.
http://www.narrowgauge.org/ngc/graphics/tkierscey/dspp/dspp0027.jpg
UpSideDownC
in New Zealand