Now I know this is probably a stupid question but are there any visible differences between the SD40 and the SD40-2?
SD40 uses the older Flexicoil trucks, which has only two holes on the sideframe between the wheels, and no center-axle snubber. The Flexicoil truck is also shorter, which means the SD40 uses a shorter frame.
The SD40-2 has a longer frame built to accomodate the newer HTC trucks, which has three holes on the sideframe between the wheels and has a center axle snubber, plus the traction motor yoke on the inboard side of the trucks that made it longer. That’s why the SD40-2 is a few feet longer than the straight SD40.
Other distinguishing features: Rear cab roof overhangs are present on the dash-2, and the Dash-2 also has a water sight glass on one of the long hood doors on the engineer’s side.
Hope this helps.
Thanks LongIslandTom!