He is reserved, makes contingency plans, strong willed, EXTREMELY judgmental, tough minded, logical, extremely serious about loyalty, enjoys his alone time.
I would say he's definitely INTJ, for the well-articulated reasons given - but a more interesting question would be, what type is Don Corleone(Brando's character?)?
My gut says: ISTP. The I is obvious, as is the T. He seems to be more tactical than strategic/ introspective. He seems fine with unexpected situations, as well as unlikely to pass judgment (like when he steals the carpet), wheras INTJs seem to have difficulties with variables outside of their carefully laid plans and have very strong opinions. He is also comfortable with a gun (typical crafter trait) the very first time he uses it (killing the local boss), as opposed to Michael, who prefers a carefully laid plan, along with some coaching (when he kills the police chief). He also seems more fun-loving than Michael (e.g. at Sonny's wedding), who rarely smiles and is permanently focused on his objectives. His strengths are complementary to Michael's, and there is a resulting mutual admiration between fellow thinking utilitarians, especially since the other two sons are Fs.