Width of the railcar and allowed overhang. A quick search, I was finding D7 and D8 blade widths, may be 12 ft, ??? I've seen large dozer blades trucked separately from the tractor. Track cleats are aggressive, addition 2" or 4" wood may have been added to protect existing flat car wood flooring. At least under the tracks, not necessarily the whole deck. Long Lumber would be install parallel with the length of the car. I've seen old tires used to protect truck/trailer wood decks, when loading a dozer.