P 344 of Vol.II of The Northwest's Own Railway features a picture of a Great Northern 0-6 2-8-2 on the line between Klamath Falls and Bend, Oregon with 4 DRGW 47 gondolas, two of which have side extensions with gaps between the wood boards. The extensions appear to be 4 feet high. Would these cars have been used for sugar beets? The gaps are far too large to be for sawdust and problematic for coal.
Utah coal traveled that route in DRGW gons for many years. The cars you mention may be in coke service as coke is a lot lighter than coal.