Melt butter in cast-iron skillet over low heat. Remove from heat and stir in sugar. Arrange pineapple slices over sugar mixture. Place cherries in center of each pineapple slice. Sprinkle with nuts.
Add reserved pineapple juice and 6 oz. can of pineapple juice together to make 1 1/3 cups juice (If not enough, add water). Pour into large mixing bowl. Add cake mix, eggs and oil. Beat at medium speed until well mixed. Pour over fruit in skillet.
Bake 35-40 minutes or until wooden pick inserted in center comes out clean. Remove from oven and let cool for 5 minutes. Carefully loosen edge of cake with knife. Invert onto serving plate.