I wondered about the end as well and just did a little digging. I found this:
https://en.wikipedia.org/wiki/1966_24_Hours_of_Le_Mans
I know, I know, you can't believe everything on the internet, but this seems to support what happened in the movie somewhat. I would think that if it was true Shelby would've made a lot of noise, but maybe with the relationship with Ford he didn't. I don't know, just speculating. Maybe now with the movie out a lot of people will dig and we might find out the details.