PRSL,
Being kind of neutral on the Rio Grande, I don't really know why the ties were 6'8" long, perhaps the D&RGW got a deal from Koppers on some meter gauge ties or ties for Newfoundland.
I do know what they were used for, though. These ties were inserted all along the 4th Division, some never even being spiked in, to show a greater accumulated loss when the case of the Alamosa - Durango line was presented before the ICC.
What happened to these ties? The ones from Antonito to Chama were left in place. The rest has served their purpose and were scrapped with the rest of the line.
At least that's the tale that came back to me when I showed some people the slides that I took of these gondolas.
Rick