Standard lane widths in North America are 12 feet. I think you will find that the 40' width figure includes the sidewalk and curbs.
40' width is the roadway for traffic.
JFK appears to be in the middle of the middle lane:
He does not appear to be left of the centre of the lane.
The right side of the car is about in the center of the lane. Cutler and Roberdeau have JFK a little to the left-of-center. But you know more than anyone else, so never-mind.
The car was 76.8 inches wide (6'4.8") and tires are about a foot to the right of the lane marker, so the right edge of the car is almost 7.5 feet right of the left lane marker.
I think you meant 78.6" wide. But if you think Ford got it wrong all these years, write them.
The tire distance to the lane stripe isn't the side of the car distance. The tire is not on the same plane as the side of the car. With Z170, for example, I don't think the widest part of the left side of the left-front tire is in view and we can only see the tread, which is inward from the car side more.
So show us your plotting!
I suggest you use a map that's somewhat accurate.
But you know more than what aerial photos can tell us, so never-mind.
And show us why JFK was not visible between the lamp post and Thornton sign! You can't use the FBI May 1964 recreation because it uses he wrong car and with the tree looking very much fuller than it was in late fall 1963.
A white Continental seen through foliage is not the same either. There's no discernible change in the foliage.