Welcome back, Johnny! I always love it when you make erudite comments about cars!

As you know better than I, the "big car" is a '39 Cad, and the one that trails Michael when he courts Kay in New Hampshire after he returned from Sicily is a '47. The '39 had to be Vito's choice, and the '47 may have been Vito's choice. It was chauffeur-driven, and, presumably, the chauffeur was probably one of Vito's trusted men, since he probably figured Michael needed to be closely guarded at that time. Later, we see Michael driving his own car, a '54 Packard Clipper. So, it very well could be that Michael was asserting his independence from Vito, or simply avoiding the usual Cadillac/mobster cliche.

I assume that production designer Dean Tavoularis selected the cars. He (or whoever else selected them) did a superb job. Anyone in films can get Cadillacs from agencies that specialize for Hollywood, and can put mobsters in them. But it took real thought (and searching) to find that Packard. There were other triumphs, too: the '43 Alfa Romeo 6C2500 that Appolonia gets blown up in; the '54 Imperial limo that delivers Michael to Moe Green's hotel; the '57 Mercury Montclair that drives Michael around in Cuba (complete with the tinny European horn so beloved of Hispanic drivers at the time); and--triumph of triumphs--the '58 Imperial Ghia limo that takes him back to his estate. Fewer than a dozen were built-where the hell did Tavoularis find one in running condition? The background cars were wonderful, too, and every one of them was not only authentic for the time, but authentic for the purpose (like the '58 Plymouth Plaza taxi that brought Fredo to Michael's Havana hotel, and the '58 Ford Custom 300 that Michael drove in Miami--exactly what Mr. Avis would have rented to you at the time).