I agree with Turnbull here.

I think Vito Corleone was meant to be a composite of the heads of the five New York families at the time.

This opinion, BTW, forms the basis for my argument that the Corleones were a fictional sixth family, and Puzo deliberately constructed Vito Corleone as a character who could not be identifed for certain as the head of one of the five families, all of which existed in reality at the time the book and film were set, as well as the time when the book was published and the film released.