In 1917, Sumpter Valley Ry built a new class of box cars, that were larger than previously on the roster at a cost of $908.36 each.
These would be a total of 5 1600 series cars like we see in the attached shot of #1604.
They were 36' long, 8' wide and a height above the rails of 11'5", (7'5" inside).
They had a capacity of 60,000 lbs, with a light wt. of 24,000 and road on Vulcan "Bettendorf style" trucks.
In 1939 #1602 and #1604 had their floors lined with steel for hauling ore concentrates.
All 5 of the cars lasted till retirement of the mainline in 1947, when they were sold and shipped to LaCeiba, Honduras, Sep. 1947