In large saucepan over low heat, combine sugar, egg yolks, flour, pineapple juice and lemon juice. Stir and cook until thickened. Remove from heat.
While sauce is cooking, bring a large pot of lightly salted water to a boil. Add pasta and cook for 8 to 10 minutes or until al dente; drain and rinse with cold water.
In large bowl, combine cooked mixture with pasta and toss to coat thoroughly. Refrigerate 8 hours or overnight.
Toss pasta with pineapple, mandarin oranges, maraschino cherries, marshmallows and whipped topping. Refrigerate until serving.