Combine the milk and rice in a large saucepan. Cook, stirring, over medium-low heat until the mixture boils and thickens, about 25 minutes. Stir in one third cup maple syrup and cook 10 minutes more. Add the orange rind and vanilla. Pour into 4 (8-ounce) dessert bowls or custard cups; then allow to cool at room temperature. Meanwhile, heat the walnuts in a small heavy frying pan over low heat, stirring, until fragrant, about 3 minutes. Drizzle with remaining 2 tablespoons maple syrup. Cook over medium heat, stirring, until the syrup boils and coats the walnuts, about 2 minutes. Sprinkle on the puddings.