Remember - one of the most intriguing aspects of GF I - III is that real mafia history is incorporated into the fiction of the Corleone story. Without that, any GFIV version will not fit with the others.

"...And I will strike down upon thee with great vengeance and furious anger those who attempt to poison and destroy my brothers. And you will know my name is the Lord when I lay my vengeance upon thee."
- Jules' version of Ezekiel 25:17