Beat the eggs in a large bowl. Add orange juice concentrate, milk, sugar, vanilla, salt, and orange rind and mix well. Dip the bread into the egg mixture, turning to coat all surfaces. Place in a baking dish in a single layer, pour any remaining egg mixture over the top. Cover, refrigerate 2 hours or overnight. Melt butter in large skillet or griddle over medium heat. Add the slices of bread and cook until browned on both sides. Arrange on a platter, sprinkle with confectioners' sugar, and garnish with orange slices. Serve with warm maple syrup. Serves 4 to 6.