No, you can't practically turn a 1964 4-door Impala into a convertible. It's not a matter of simply removing the roof; the structural integrity of a 4-door sedan is completely different from that of a convertible. Convertibles are built with reinforced chassis and body structures to compensate for the lack of a roof. Cutting the roof off a sedan would leave it extremely weak and dangerous to drive.
The engineering and fabrication required to create the necessary reinforcements and modifications would be incredibly complex, time-consuming, and prohibitively expensive – likely far exceeding the value of the car. It would essentially involve building a new convertible from scratch, using parts of the existing car.
