Combine dried plums and 3/4 cup port in a small saucepan; bring to a boil. Reduce heat; simmer 15 minutes or until plums are tender. Let stand 5 minutes. Place plum mixture and 2 tablespoons water in a blender. Cover tightly, and process until smooth.
Combine 1 cup milk, 1 1/2 cups water, rice, and salt in a medium saucepan; bring to a boil. Cover, reduce heat, and simmer 25 minutes. Stir in 1 cup milk, granulated sugar, and vanilla. Cover and simmer 30 minutes. Remove from heat; let stand 10 minutes.
Spoon about 4 teaspoons plum sauce into each of 6 (6-ounce) martini or parfait glasses; top each serving with 1/3 cup rice pudding. Repeat layers once. Cover and chill at least 4 hours.
Combine whipping cream, 2 tablespoons port, and powdered sugar in a medium bowl; beat with a mixer at high speed until light and fluffy. Top each serving with 2 tablespoons cream mixture and 1 teaspoon slivered almonds.