There 2 are at least Nardi Alfa 6c2500 coupes. The model of silver car with race #646 from the 1949 Mille Miglia is chassis 9484. Disregard the other color variations on the model.
Somewhere I have a photo of the car in front of a Nash dealership. Supposedly, a Nash stright 6 was to replace the Alfa motor. I don't know if this ever happened, but a GMC or Chevy straight 6 was put in the car, and it did run that way in the US.
Supposedly this car was sitting in Kagel Canyon, north of Los Angeles, but I looked many times and could not find it. According to the records John sent me, the last known appearance of this car was on the east coast.
I'm not sure of the chassis number of the red car with race #647, also from the 1949 Mille Miglia. You can disregard the other color variations on this model too. I have no idea what happened to this car.
There may have been a third coupe car that looks virtually identical to the first, silver car. I'm saying "may have been" as various photos I have of the car show a number of detail differences. It might be the same car modified..
model of silver car race #646:
www.alfamodel43.com/Alfa Romeo 6c 2500 Nardi Danese 1° Serie
model of red car race #647
www.alfamodel43.com/Alfa Romeo 6c 2500 Nardi Danese 2° Serie