In a small saucepan, combine orange juice, sugar, cornstarch, lemon juice and butter. Heat, stirring, until thickened; cool. Fold into whipped cream. Chill until ready to serve. Add enough water to reserved pineapple juice to measure 1 cup and set aside. Cut pineapple chunks in half; set aside. In a medium saucepan, soften gelatin in 1/2 cup orange juice for about 1 minute. Stir over medium heat until gelatin dissolves, about 1 minute. Remove from heat and add remaining 1/2 cup orange juice and reserved pineapple juice. Chill until consistency of unbeaten egg whites. Fold in reserved pineapple chunks, apple, celery and nuts. Pour into a 3 1/2 -cup mold and chill until firm, about 3 hours. At serving time, unmold on a lettuce-lined plate and serve with the following dressing: