Thanks for doing a test-run on my process. Of course, the result would imply that the adjacent truck on the hopper would also have a 6' - 6" wheelbase, since you demonstrated that they match.
While the journals, wheel faces, and car sides aren't in the same plane, they're pretty close in this picture. I'm guessing the car is at least 500' from the photographer. The difference in distance from the car side to the wheel face is 2 1/2 feet. So the "correction factor" would be .005.
And the car angle isn't so far off that the proportions of the dimensions of interest would not still be linear. I think. As the "length" of the car side shrinks with rotation, so does the "length" of the wheelbase. Proportionally.
My continued re-examination of this photo has revealed to me a steam locomotive cab, in the foreground, that appears to be used for a warm-weather break room (no heat, covered windows). And judging by the remaining snow, warm weather is still in the future.
A wonderful photograph.