It has kind of already been said, but to reaffirm: If you have a battery charger, you already have a bench test power supply. You can test anything on an old truck with a Charger. You can use an inline fuse if desired.
FIY: You don't test a switch with a power supply.
I agree with your opinion on the radio.
For what it's worth, my opinion: I don't like the radio on when I drive old trucks and they are AM only. Possible weak reception. They are great for filling the hole. You may consider using one for aesthetics. As thrilling as it is to get something N.O.S., a radio is not one of them. The refurbish cost is the same. Possibly sell yours and make a few bucks, buy a non runner, or a face, to fill the hole.
They do make modern look-a-like radios.
