Recommendations for a car stereo set-up?

The trapezoidal opening can be corrected very easily with a die grinder. The factory radio faceplate will even cover the alteration if you reinstall the original sometime later. Of course it is real hard to find the shaft mount style of radio to fit the 60's era dashes.

I am basing this on a 65 valiant, I know that on a 66 dart the radio bezel is much much larger and is not something you want to alter if you are concerned with originality.