|   4 cups sliced fresh plums  1/2 cup sugar  1/4 cup all-purpose flour  1/4 teaspoon salt  1/4 teaspoon ground cinnamon  1 tablespoon lemon juice  1 (9 inch) unbaked deep dish   pastry shell  |    TOPPING:  1/2 cup sugar  1/2 cup all-purpose flour  1/4 teaspoon ground cinnamon  1/4 teaspoon ground nutmeg  3 tablespoons cold butter or   margarine  |