The trucks that are presently under the narrow frame tankcars are from scrapped UTLX frameless tankcars. The White Pass acquired these trucks at the same time they took the 15 narrow frame cars north. It seems that the newer trucks were stronger then the older arch bar type.
As far as we know there are only three sets of the original UTLX arch bar trucks still in existence. Two sets in Chama that where under the water cars (ex-UTLX narrow frame tankers) and one more set at the Sumpter Valley Ry. that goes with their #100 tankcar.