Half the fun for a saddo like me was trying to identify the tracks used instead of the actual tracks that have long since gone.
Did you work out what the tracks were? I think the Riverside shots were done at Willow Springs & Road Atlanta was used for most of the Le Mans shots. I understand the Mulsanne Straight stuff was done on a public road in the US.
In case you missed it there was a documentary on BBC4 last week about the making of the Steve McQueen Le Mans movie, should be able to get it on catch-up.