This recipe is from 1978.
Creamy Italian Salad Dressing
In a bowl, combine one envelope of Good Seasons Italian or Bleu Cheese Salad Dressing Mix with with 1 1/2 tsp. vinegar and 1/3 cup of water; mix well. Add 1 1/4 cups mayonnaise; mix with fork until well smooth. Cover; refrigerate. Makes 1 1/2 cups.