Preheat oven to 275°F. Grease and flour two 9x5-inch loaf pans, then line with parchment paper.
In a large bowl, toss candied fruits, raisins, and nuts with 1/2 cup flour until evenly coated. Set aside.
In another bowl, whisk together remaining 2 1/2 cups flour, baking powder, cinnamon, nutmeg, allspice, and salt.
In a large mixing bowl, cream butter and brown sugar until light and fluffy, about 3-4 minutes.
Add eggs one at a time, beating well after each addition.
Combine orange juice and molasses. Alternately add flour mixture and orange juice mixture to the butter mixture, beginning and ending with flour.
Fold in the floured fruit and nut mixture until evenly distributed throughout the batter.
Divide batter evenly between prepared pans, smoothing the tops. Place a shallow pan of water on the bottom oven rack.
Bake for 2 1/2 hours, or until a toothpick inserted in the center comes out clean. Cover loosely with foil if tops brown too quickly.
Cool in pans for 30 minutes, then turn out onto wire racks to cool completely.
If desired, brush with brandy or rum, wrap tightly in cheesecloth soaked in liquor, then wrap in plastic wrap and foil. Store in a cool place, brushing with additional liquor weekly for up to 4 weeks before serving.