A D&RGW conductor told me that in the 1960s the D&RGW considered a "quick and dirty" standard gauging of the San Jan Extension from Antonito to Farmington , if Federal permission to abandon was denied .It would have few if any changes to the grade .Car lengths would have been limited to forty feet . GP-7s would be the motive power .I am not sure if axle loadings would be any consideration , other than on the trestles . The Leadville line and the Monarch branch are examples of a narrow gauge railroad that were standard gauged successful ,with little relocation .