Another option I did was to take a modern radio (alpine) and make the face remote mount, and put it on a panel that is under the dash, (panel also has 3 guages as well). Its set up so when I flip a switch, it retracts up under the dash and you cant see it. The "brains" of the radio are mounted in the glovebox.
When its retracted, you cant see it unless you get down on the floor, so it looks completely stock for shows, etc., but it has cd, sat radio, ipod, etc.
The one thing i like about it is that the parts that you have to remove from the stock radio (at least on a 56) can be replaced later if needed, so the original radio, while inoperable, isnt destroyed...
Just another thought.
Ron Grove
Wauconda, IL