Bring a large saucepan of lightly salted water to the boil. Add the pasta and cook until al dente, 5 to 7 minutes. Drain, transfer to a large salad bowl and cool.
Whisk the sugar, eggs, flour, salt and reserved pineapple juice together in a saucepan until smooth. Cook and stir over medium heat until the mixture thickens. Pour over cooled pasta and toss to coat evenly. Cover and refrigerate overnight, or at least 8 hours.
Stir the pineapple pieces and mandarin oranges into the pasta mixture. Mix in the coconut. Stir in the whipped cream until evenly blended. Chill until serving.