Back in 1976 I exchanged letters with Mal Ferrell regarding the Sumpter Valley cars that went to the White Pass. He provided the following information:
"The WP&R received their former SV cars in serveral batches. First, in 1942 the Unitied States Army, which was operating the WP&Y, obtained the following sumpter Valley cars: Date of Sale was 8/30/1942:
SV Flates: 76600, 76614, 76617, 76628, 76633, 76640, 76646, 76661, 76668, 76680
"At this same time, the SV sold to the Army the foolowing cabooses:
SV Cabooses: #3 sold 7/28/43 to U.S.A. and distroyed in rodundhouse fire of May 11, 1946.
................... #4 sold 7/28/43 to U.S.A., not used by WP&Y and sold as a outbuilding in Skagway, Ala.
"About this same time, the U.S.A. purchased the two "turtle roof combines form the SV for use on the WP&Y:
SV Combination car, St. Charles Car Works, ACF #10 to WP&Y 209
SV Combination car, St. Charles Car Works, ACF #10 to WP&Y 211
"Later on, the WP&Y purchased the remaining St. Charles Cars from the Sumpter Valley:
SV Baggage/Mail #5 became WP&Y X-3
SV Coach #25 became WP&Y 266 (Parlor car)
SV Coach #26 became WP&Y X-12"
Hope this helps.
Brian Norden