Preheat oven to 350 degrees F.
Crumble the bread by hand into a large mixing bowl. Melt the butter, then pour it over the bread crumbs. Add the seasonings and chopped celery. Then mix with the deboned chicken chunks.
Turn into a large roast pan and bake covered for a half-hour to an hour, until heated through. Dampen with water around the edge if it begins dry out. Stir often to prevent sticking.
Giblet Gravy: Cover heart, neck and gizzard from chicken with about 5 to 6 cups salted water, bring to a boil and cook until tender, about 1 hour. Add liver and cook an additional 10 minutes.
Lift meat from broth and cool. Cut into small pieces and set aside. Pour broth into bowl and set aside.
Melt 4 tablespoons butter (or equivalent amount of drippings from chicken roasting pan) in pan where giblets were cooked. Add 1 tablespoon flour for each cup of reserved broth. Brown flour slightly.
Stir in reserved broth over low heat, stirring constantly until gravy is smooth and thickened. Add giblets to gravy and warm. Serve over mashed potatoes and filling.