The radio will be a major deal..due to grounding..I for that reason and consideration of AC install did not install it. Besides, the old radio tough neat in looks is not really a useable item. (quality stations are not comon IMHO) Mount it, hook up the light for looks, mount an aftermarket good stereo out of sight. Actually if you go with 12 volt, go with negative ground, change all your bulbs, use a Runtz resistor on the blower motor and if electric wipers, use one there, you can build a variable regulator that is about the size of a small match box that is positive ground as it is so isolation is an issue..this unit will handle 12 amps of continious curent, surge to 15 amp. I have one in my car and is negative ground, thus I have it isolated. Be sure your iso box is well vented. This device will fold if shorted and not burn out...
As you can see, the device is self contained, the control circuit and filtering is external and small enough to solder on the socket. The red rectangle is the variable resistor for adjusting the voltage...the heat sink is a must. If you iso-mount, be sure the box is drilled for good ventialtion.