Builder? Thrall? 66 foot 3564 cu ft mill gondola
Union Pacific 66' 3564 cu. ft. Mill Gondola (18 ribs per side)
Other prototype data needed. More photos?
This looks very similar to the Exact Rail HO scale model that has 18 ribs (attachment). This appears to be similar to a Greenbrier gondola however the Greenbrier has 17 ribs per side.. See drawing attached.