Since your car was delivered without a radio, I would guess the dealer probably would have installed either a Becker Europa TR, or a Blaupunkt Frankfurt. Or possibility just sold it with the radio delete plate. No way to know for certain but these were the two most common dealer installed radios. Possibly a Becker Grand Prix? As for antennas, either a Wisi, Fit or Hirschmann though other brands could work.
What I’d do is determine the opening size on your dash and then try to find a Becker or Blaupunkt that would work. Match the knobs on the radio to whatever style knob is in your car (cigarette lighter, windowcranks, etc.) Going this route should satisfy most concourse judges if exhibiting your car is one of your intentions. Certainly the car would appear stock.