Frank,
Guess your direction in 3ed sentence was intended to read Westward (1.42%).
As I see it, the revenue capacity is the #487 westward load limit to Cumbres and not the climb up the 4%, PLUS even what extra it can handle down grade back to Antonito. Store all surplus available equipment at Cumbres and always dispatch from Antonito with maximum load limit. Leave cars at Cumbres which can not be pulled back east out of Chama. Add as many cars to EB train that can be loaded at Cumbres by local parking or by bus connection from Chama or Antonito. As the surplus cars build up at Antonito that can not be handled on the WB revenue train, advance them back to Cumbres by a one way extra, probably twice a month depending on demand and number of active cars in fleet. That WB "Cumbres Turn" could also be sold as a special excursion, with bus return.