Interesting question!
It appears to have been a faze-out in 1935-1936. My books say that half way into 1936 the doors were changed to all steel. In 1935 the steel industry perfected a way to produce a roof assembly from 80 inch width sheets, allowing for the introduction of the "turret top" roof design, a strong noise-free one piece roof. It all seems so basic now, but imagine how revolutionary it was back then. All that new steel technology was the reason streamlining could be achieved. What an amazing era in automobile design. I always thought that Chevrolet's most beautiful cars were produced between 1936-1938.
SPEEDLINE