In a large saucepan over medium-low heat, combine 1/2 gallon milk, sugar and rice. Simmer, covered, 1 hour, stirring frequently. Remove pan from heat and let rest 10 minutes.
In a small bowl, combine eggs, 1/4 cup milk, salt and vanilla. Stir into rice mixture and return pot to low heat, stirring constantly, for 2 minutes. Pour into a 9x13 inch dish and cover with plastic wrap, folding back the corners to allow the steam to escape.
When pudding has cooled to room temperature, remove plastic wrap and sprinkle surface of pudding with cinnamon. Cover tightly (with fresh wrap) and refrigerate 8 hours or overnight before serving.