I need to see the movie again and check out the cars in the last scene.

HOWEVER car production during the 40s was completely devoted to the war effort, so folks held onto their vehicles. And not everyone drives a new car (my current car is 10 years old, my previous car made it 18 years) so if I'm not totally sold on the car date = date of the scene theory. (Not that they'd be driving 1940s cars in 1970, but it does get us into the 50s....)