You can remove the cover and look at the tubes. The tube numbers start with 6 for 6 volt and start with 12 for 12 volt. If I remember correctly, your radio will be similar to this 12 volt version.
1955 Chev Truck Radio You should test the radio with a 6 volt source if it is six volt. Seeing the new orange capacitors is a good sign. You may have a power wire for the dial light and a separate one for the main power. It may also only have one power wire. I probably have the correct information for your radio and I could send it to you by Email.