Soften gelatin in cold water. Add boiling water, sugar, and salt; stir. Add juices and rind and stir again. Refrigerate 2 to 3 hours or until slightly jelled and the consistency of unbeaten egg whites. Break cake into small pieces and set aside. Whip 1 cup of cream and fold into gelatin mixture. Line a 2-quart bowl with waxed paper. In lined bowl, put layer of cream mixture and layer of cake cubes. Repeat, ending with cream mixture. Refrigerate 8 hours or overnight. Invert onto cake plate, peel off paper, and frost with remaining whipped cream. Sprinkle with nuts and coconut if desired.