After thinking about it again it becomes evident that most likely the N338 isn't part of the movie opening. Because it still is the main road to Tours I don't think the character of the road will change completely south of Mulsanne to a tiny narrow road. Therefore the road from the movie doesn't even have a central reserve.
Here are two pictures from 1969 that show the end of the Mulsanne straight before the cars turn right towards Arnage. One from a spectator's (#1) and one from a drivers (#2) point of view.