Note that the 30" wheels are for the 1890 #2 Plow. I think that the photo of the two trucks is more interesting. The rear truck has 33" wheels but no description of the front truck wheel diameter is given.
The front truck appears to be sloped and has the front wheels smaller than the rear. There are programs to rotate and skew the photo so that a comparison could be made based on the known short wheel base. Just a thought.