Since the new mill gondola is 65' or 66' long then the 1968 scheme for the ILLINOIS CENTRAL's IC 97350-97499 65' gondolas built by Bethlehem Steel can be applied to these O scale models. If you can find builder's photos from 1968, then you can reproduce accurate graphics.
The CN/IC is still using these gondolas. Many have been repainted in the CN/IC scheme in Illinois.
Andrew