My 1955 TBird was converted to a 12 volt electrical system before I bought it.  I have the engine out of the car.  I removed the battery tray to clean the frame and clutch linkage.  The battery tray has been modified (crudely) so a wider 12 volt battery will the 6 volt tray.  Can I swap in a battery tray from a 56 or 57 Bird to fix this problem or do I need a special 12 volt battery?