I have very few BNSF shots, but here's one from October 2011 at Simpson, SC which includes a UP unit too. The NS units are in the hole with their train.
If you are asking about the orange box behind the cab on the 733, that's an air conditioner from a like unit that had already been painted in the new colors. Seems it was normal shop practice to pull an A/C unit and replace it with one that had already been repaired so it was common to see orange A/C units on war bonnets.
Thanks, had seen Roof Mounts and knew of Engine compartment units, had not seen essentially fender mounts.