If you want to spend some money, the following sites have topographic maps from the 1970s-90s for varying prices: -
http://www.omnimap.com/catalog/int/poland1.htm#p7
https://mapstor.com/map-sets/country...1989)--preview
If you're not so keen to spend money, these links have maps of various utility: -
Map: Poland - Time: 1967 - Scale: 1:1,250,000 - Note: large download size
https://www.davidrumsey.com/luna/ser...205445~3002423
If nothing else, this map will give you a good comparison to check for changes from the 1940s maps. (On this particular map, find Warsaw in the top right-hand side, then head S-W to Lodz, then move slightly West to find Kalisz).
Map - Krakow and surrounds - Time: 1956 - Scale: 1: 500,000 - Note: large download size
http://legacy.lib.utexas.edu/maps/am...akow-232-a.jpg
Same story as map above, doesn't show small detail but gives a good overview of the region in the 1950s. (On this map, locate Lodz in the top right-hand corner and travel slightly West to find Kalisz).
This map may be some help as well. It shows land use as of August 1990. You can see that a lot of Poland is used for agriculture and forestry. Even in 2010 (I was in Poland for about a month in 2010), they were barely growing enough food for their own consumption.
https://legacy.lib.utexas.edu/maps/a...nd-landuse.jpg
And there's this tactical pilotage chart from 2001 that covers a wide section of Poland. Again, the download size is rather large.
Scale: 1:500,000
http://legacy.lib.utexas.edu/maps/tp...34566_e-3d.jpg
On this map, find Warsaw in the top centre of the map, head S-W to locate Lodz and again travel slightly W to find Kalisz.
Hopefully with those three maps, you can chart any significant increase in town sizes compared to the 1940s maps. From a quick glance, I would say that generally, watercourses, road & rail have barely changed locations (if at all).