The go-kart is an old Le Mans racer. Probably pre-1969. You can tell it's a Le Mans car, because it has the headlight for night racing, and still carries the "luggage box" the Automobile Club de L'Ouest mandated to prove it was a road-going passenger car.
Slicks came around in 1970, so the treaded tires in the rear show it's age as 1969 or earlier. Front tires are obviously non-original.
After the huge Cadillac custom-bodied racers that Briggs Cunningham ran in the 50s, there was an effort to downsize and compete with the Europeans on maneuverability. It may be a car born of that design specification.
An excellent piece of history. I'd buy it for sure.