I've never seen this done on an automatic car. Theres mechanisms in the shifter if cut could prevent you from shifting. Probably a cable or something.

As for the indash radio why not just buy a a radio with a built in 7in screen.
Panasonic, JVC, Kenwood makes them.

I have done the method your describing on my car and i wish I originally bought that indash screen but ohh well.

I bought my fiancee the JVC 6.5in tv/ radio etc...for her car and she loves it.