Does the museum have copies of any of the maintenance logs from the era? I imagine Fort Lewis might have the RGS log books from that time. Anyone up to doing some research? I would but I'm over 2000 miles away.
When was it said that the D&RGW turned the flanges? Wouldn't they have decided to turn them to be standard unless the RGS asked for them to be turned half-flanged? How about the territories the 346 operated in those years? Would the Grande have decided that they need a C-19 capable of working the light track / bridges (i.e. west of Gunnison) on poor track? Maybe the shop men, since they had to turn the tires, just did it to keep the engine and train men off their backs...
Who knows? Like some said, it might have been a far easier fix than the suspension...