Lots of info here, most right, some wrong. The guess that the base set might be the 20320 from 1957 makes sense, but the 5620T from 1956 was identical. Both sets came with the 928 lumber car, 925 Gulf tank car, 937 MKT box car, and the 977 action caboose. The 1957 catalog incorrectly shows the caboose as the 979 action caboose but this is incorrect as all known sets supposedly had the 977. The third picture appears to show the brass railings and ladders on the caboose, a tip-off that it's a 977. The locomotive is definitely a plastic C&NW Pacific. Most sets had the 283, but a few 1957 sets had the identical locomotive numbered 21084.
As far as boxes go, the set quite possibly was originally packed with the blue/yellow boxes (the ones with the 1947 copyright date), but the later red/white boxes were also used with 3-digit components. Several of the 1956 sets came with the red/white boxes.
It's great that the photos were saved to remind everyone of those wonderful trains!
