I was at Don's house in 2014. He had both the white 4-speed coupe and the black 4-speed convertible at that time..
He did not claim the convertible was an original 4sp car, only that when that he bought the car, it had all the rare 4speed parts in the trunk, including the bellhousing, transmission and headers. The parts possibly came from a Facel-Vega or maybe a factory-built 4-speed 300F otherwise lost.
Maybe not original, but I wouldn't mind owning it.