In a small sauce pan, combine the sugar, flour and salt. Gradually stir in pineapple juice. Bring to a boil, stirring constantly. Stir a small amount of hot mixture into eggs; return all to the pan; stirring constantly. Bring to a gentle boil; cook and stir 2 minutes longer. remove from the heat. Gently stir in lemon juice.
Transfer to a bowl. Cool to room temperature without stirring. Cover surface of dressing with waxed paper; refrigerate until cooled.
Cook pasta according to package directions; drain and rinse in cold water. Place in a very large bowl; stir in the oranges, pineapple, marshmallows, coconut and dressing. Fold in cool whip. Cover and refrigerate until chilled.