If you are loading PS-2 hoppers, you only need to backdate to 1957, since, to date in N scale, no one has produced a PS-2 from an earlier date. And IIRC, the "earliest" PS-2 dates from 1953 or 54, unless perhaps a demo car was being shown around a year or 2 earlier.
But in general, any sort of industrial structure won't look too much out of place if you weather it appropriately- which in this case, means "not too much". A lot of companies worked through World War II with a combination of facilities built in the 1920s and makeshift floorspace added to increase wartime production. By the time the war was over, those old factories and equipment were worn out, and the makeshift spaces in need of conversion into permanent, up to date structures. So, even though the economy was not always booming, a lot of production capacity was replaced or rebuilt in the 1950s. Look what happened with railroads- it took years for Pullman and ACF to catch up on orders for boxcars, gondolas, coaches, even sleepers, and EMD and other builders couldn't keep up with orders for diesels, as railroads modernized from 1946 to 1960. The same was true in mining, materials production, electronics.
So, I don't know just looking at it when the prototype for that structure was built (1970s?), but take a look at photos of stuff that was under construction circa 1957, and I think you'll find that with some detail changes, you'll be able to backdate the structure enough that it won't look out of place.
