Preheat oven to 300°. Line a 9x5-in. loaf pan with parchment, letting ends extend up sides of pan; grease and set aside., In a large bowl, mix the flour, baking powder and salt. Add the walnuts, dates, cherries and mangoes; toss to coat. In a small bowl, whisk the eggs, brown sugar and 1/2 cup rum until blended; stir into fruit mixture. Transfer to prepared pan., Bake until a toothpick inserted in the center comes out clean, 1-1/4 to 1-1/2 hours. Cool in pan on a wire rack 20 minutes. Slowly pour remaining rum over cake. Cool completely. Wrap tightly and store in a cool, dry place overnight. Cut with a serrated knife.