Combine chicken with water, 1 teaspoon salt and celery tops in a large saucepan; heat to boiling; cover.
Simmer 1 hour.
Remove from broth and cool until easy to handle; strain broth and chill for soup or gravy.
Pull skin from chicken and take meat from bones; dice. (There should be about 2 cups.)
Place in a medium size bowl.
Drain syrup from pineapple into a cup.
Add pineapple and grapes to chicken.
Blend 2 tablespoons of the syrup with 1/2 cup mayonnaise or salad dressing and remaining 1/2 teaspoon salt in a small bowl; fold into chicken mixture.
Chill.
Halve avocado; pit and peel.
Mash in a small bowl; stir in crumbled bacon, 1/4 cup of the remaining mayonnaise or salad dressing and red pepper seasoning. (Fix avocado mixture no longer than an hour ahead so that it keeps its bright color.)
Cut each loaf of bread lengthwise into 3 even slices; spread with remaining 1/4 cup mayonnaise or salad dressing.
Spread avocado mixture on bottom slices and chicken salad on middle slices; stack loaves back in shape; cover with top slices.
Cut loaf crosswise into 8 thick double decker sandwiches.