There are several shots in the Steve McQueen film (which is post Ford pre Porsche) where they look left from the pits and the road is blocked by straw bales beyond the Ford chicane, and hence you can see that the pit straight used to come from Maison Blanche. Until this year, with the new Ford/MB grandstand bypass, you could see the old road running past the grandstand. You could stand there and it all made sense (sorry if this doesn't)
The other major change, after the Porsche curves and the loss of the Pontluie hairpin (yes the Bentleys went past Carrefour) is the pit straight and esses section. I know this was rebuilt in 1955/6, but were the pits bypassed at this stage, (as the pit straight is the original road) and the esses must have been bypassed by the dual carriageway some time later.
I've read this all somewhere, it may be the book by Clausager