It would be interesting to learn how and why that car got from California to Luxembourg. I have trouble getting things from the USA to Pender Island BC, I can't imagine what it took to get that car to Luxembourg.
These cars were not known as gasoline misers but 9MPG? that's a bit much. I only got about 6MPG in my GTO but it had really steep rear gears. Do you know what RPM you were turning at 50 MPH?