There are several very large buildings in this collection, and the post office is one of the largest three.
The side of the box reads, "The people of Bedford Falls knew they were a city of some substance when the new Post Office was built just after World War I. Located near the railway station, it has been a link between Bedford Falls and the rest of the world. During World War II, just recently over, it was the center of activity in the town."
Well look at that, the box gives me a clue for where to look. It's amazing that in all of the years of owning this collection, I have never read the building descriptions on any of these boxes.