1. In a bowl, mix raisins, candied peel, and 1/4 cup rum. Let stand 20 minutes.
2. Meanwhile, grate peel and squeeze juice from 1 orange and the lemon; reserve. Thinly slice remaining orange, discarding ends; cut slices into half-moons. Arrange slices attractively over bottom and up sides of a buttered 9- by 5-inch loaf pan.
3. In a bowl, with a mixer on medium speed, beat butter and sugar until well blended. Add eggs, one at a time, beating well after each addition. Add grated orange and lemon peel and 2 tablespoons each orange and lemon juice (reserve remaining for other uses).
4. Add flour, baking powder, baking soda, and salt and beat on low speed until well blended. Stir in rum-steeped raisins and candied peel. Scrape batter into prepared pan, taking care not to disturb orange slices; smooth top level.
5. Bake in a 350° oven until a wooden skewer inserted in the center comes out clean, 50 to 60 minutes. Let stand 10 minutes, then run a knife blade gently around edges to release cake; invert onto a wire rack.
6. In a 1- to 2-quart pan over medium heat, stir marmalade and remaining 2 tablespoons rum until hot. Pour through a fine strainer into a small bowl. Brush glaze all over warm cake. Let cool to room temperature, about 1 hour, then cut into slices to serve.