The Port of Entry photos appear to be on Valley Drive and it was operated by the Montana Highway Department (blurry fine print on the bottom of the sign). The tracks, grade and skyline in the photo match. The location was directly across the road from where the old Red Rock Sporting goods was, I think the floor of the office is still there, along with a concrete driveway in front of it (apparently added sometime after the photo). Check google earth/maps, probably shows up. Another possibility is directly across the road from the USDA building a couple hundred yards further.