Im pretty sure its a 52 Nash Healy (i know someone already said it, but hey i got the year right...i think )
JDub's last car wasn't really a Fiat, it was an Autobianchi, and it wasn't from 1950, it was late Fifties. The car that Sonny was driving when he got nailed in "Godfather 2" was a Lincoln, and I don't think this car is a Lincoln, but I'm pretty poor on the old American cars.