There were many more differences:

The Dash-2 frame was longer - 65-8 vs 68-10

Unless salvaged trade-in trucks were used, the HTC truck on the Dash-2 had all the traction mtors pointing in the same direction. This did not change the truck wheelbase, but the truck frames are longer with an inboard extension towards the fuel tank to support the third traction motor. This was done to make them less prone to weight transfer when pulling hard. A spotting feature is the hydraulic shock on the center axle. Also three holes in a group are visible in the sideframe on an HTC vs two on the older truck.

The various "block boxes" of electronic devices used on the 40 series to control the aux gen, excitation, wheel slip, dynamics and other functions and options were divided into modules. A module can be replaced under a minute without disturbing any wiring.

There were changes to the toilet access and nose, radiator fans (later Dash-2s have Q-fans), and the radiator intakes/core arrangement, but I don't believe these correspnded with the Dash-2 change.