In small heavy saucepan, beat egg yolks, slightly; add reserved pineapple syrup, sugar, vinegar, butter or oleo and salt. Cook and stir over low heat about 6 minutes or until mixture thickens slightly and coats a metal spoon. Cool to room temperature. Combine drained pineapple, cherries, oranges and marshmallows. Pour custard over and mix gently. Fold in whipped cream. Put in serving dish, cover and chill 24 hours or overnight. Garnish with fresh mint leaves and extra sectioned oranges, if desired.