Installing a new stereo in the dash...help please..

I'm in the process of redoing my dash completely. I filled in the original heater control opening, am going to move the original radio opening over and cut it to accept a single DIN, and then cut out for the Vintage Air controls. I have never passed up buying a car due to the dash being cut. If everything on the vehicle is original then you might have a issue when you go to sell it with a modified dash.