There are 3 members of the Carson & Colorado Rwy that work at the D&S if 18 was an option it would have been discussed. I should also point out that Carson & Colorado Rwy restored and operates SP 18, but does not own the locomotive, the county does.
As has been pointed out 18 is a small loco and would not be of much advantage to the D&S. They are doing what makes the most sense converting a loco already under restoration to oil. Plus one more after that.
493 is in good hands I know 2 important people in the shop at the D&S and they know oil burners as well as they know coal.
Jeff Taylor
CRRM curator of equipment and rolling stock.