I wonder if fuel and water needs are the main reason they used 4 engines, not because it took 4 engines to push the plow? That is if 2 engines could do the job, they might do it with the bar in the corner and using all of the steam they could make, so they would be unable to make it between water and fuel stops along the line. With 4 engines all working easy they could get a lot farther on what they carried? There is a shot I have seen (probably on my computer in the few thousand photos it holds) of Eng. 50 with the daily pass. train pushing the plow up the Sumpter Valley. There probably was much less snow plus #50's tender held a heck of a lot more water and fuel than the geared engines carried.