It seems a little odd that they had to disassemble the locomotives because the ships rigging could not handle that heavy of a load.
When SVRy No's. 19 and 20 were shipped to Skagway in 1941 intact, as the photos show.
The first photo is at Skagway and the second at Seattle.
Granted the Sumpter Mikes were lighter that the 70 class, but not by that much. Also note that the ships rigging was not being used, but I would think that if dockside equipment was available in 1941 it likely was in 1938.
Photos are in the Sumpter Valley archives, from the collections noted.