Drain pineapple; reserve 2 tablespoons syrup.
To make custard, in small heavy saucepan combine reserved syrup, egg yolks, sugar, vinegar, butter or margarine, and salt.
Cook and stir over low heat about 6 minutes or till mixture thickens slightly and coats a metal spoon.
Cool to room temperature.
In large bowl combine pineapple, cherries, oranges, and marshmallows.
Pour custard over; mix fruit mixture gently.
Whip the whipping cream till soft peaks form.
Fold whipped cream into fruit mixture.
Turn into serving bowl.
Cover and refrigerate 24 hours or overnight.