Preheat the oven to 350 degrees F.
In a medium bowl, add the brown sugar, the walnuts, and 1 cup of the flaked coconut and stir to combine. Set aside.
Grease a 9x13-inch baking dish, and then, using the extra flour, lightly dust the dish and tap out any excess.
In a large bowl, add 2 cups of the remaining flour, the sugar, the baking soda, and the salt and stir to combine.
With the back of a spoon, make a well in the center of the flour mixture and add the eggs and the fruit cocktail with the juice, and mix well to combine.
Evenly pour the batter mixture into the prepared baking dish. Sprinkle the topping mixture over the batter.
Bake, uncovered, until a toothpick inserted into the center of the cake comes out clean, for about 30-35 minutes.
About 10 minutes before the cake is ready, place a medium saucepan over medium heat. Add the butter, corn syrup, evaporated milk, and the rest of the flaked coconut. Stir constantly until the mixture boils and thickens.
Transfer the cake from the oven to a wire rack, evenly pour the sauce over the top of the cake, and
transfer it back to the oven and bake until it bubbles, about 5 minutes. Do not over-bake.
Transfer the cake from the oven back to the wire rack and let it cool slightly before serving.
With a sharp knife, cut the cake into serving-size pieces, plate, and serve.