Captian Obvious Driving a cool 65 Formula S??
The modified rear glass gives the car an interesting/different enhanced "bubble" look. I always thought that Plymouth didn't quite get the back window shape quite right in production, probably because of the difficulties in casting and shaping a window of that size. If it could have been made so that the glass slopes in a completely straight line when viewed from the side, rather than being curved a bit, it would have helped sharpen the overall look of the car (making it less obvious it was "just" a Valiant with with a big back window grafted on).
Steve