There were major changes to the HH series units in 1937-38 when Otto Kuhler was brought in to clean up the styling of the units.
Dirk's unit is based off ATSF 2301, an 1937 built unit. Easiest way to tell is the feather edge at the joint between the top of the hood and the front of the hood.
I don't know for sure if Alco changed the frame when they revised the styling, but if they did that would make sense why Dirk's source shows 6" difference in the wheelbase and the C&EI and NH units show a 1'9" difference from the wheelbase of the 44 Tonner.