Going back to Cadillacs for a minute, werent all the cars at Vito's funeral chauffer driven Caddies?
I believe you are correct. I think I once read that a couple of the flower cars were "modified" Cadillac passenger cars, as "professional" cars, as they are called are not easy to find, especially of that vintage. Ironically enough, I think the hearse used was a Packard.
The last flower car is a modified 1956 Fleetwood. In other words the back part was cut to make it look like a flower car.