There was an external method to determine some radio manufacturers. I believe that because Philco was owned by Ford, the glass on those radios had "Philco" ink stamped on the inside of them. That may have been year (65 or 66) specific. Also, the tuning dial ink stamping on AM radios was different between manufactures. Some started "5", others with "56". I went thru this some 25 years ago to ID mine, but I don't remember the specifics. That too may have been year (65 or 66) specific.
Jim