Whisk the 1/4 cup oil with the flour in a large heavy skillet (preferably cast iron) until smooth. Cook, stirring frequently, over medium-low heat until the roux turns a dark mahogany brown, about 1 hour. Do not allow it to burn. Set aside.
Sprinkle the chicken with salt and pepper to taste.
Heat 2 tablespoons of the butter with the remaining 1 tbsp oil in a large heavy pot over medium heat. Sauté the chicken pieces, about half at a time, until dark golden, 8 to 10 minutes per side. Transfer to a plate.
Remove all but 1 tbsp fat from the pot. Sauté the ham strips over medium-high heat until lightly browned, about 4 minutes. Transfer them to the plate with the chicken, along with any juices.
Melt the remaining 2 tablespoons butter in the pot over medium-low heat. Add the onions; cook 3 minutes. Add the garlic; cook 1 minute. Add the celery, green pepper, and tomatoes. Cook 5 minutes. Stir in the roux; mix well. Add the chicken stock, Worcestershire sauce, bay leaf, thyme, oregano, allspice, and cloves. Heat to boiling and stir in the sautéed chicken and ham, including any accumulated juices.
Return the gumbo to boiling; reduce the heat. Cook, covered, over medium-low heat for 1 hour.
Add the okra and cook, uncovered, 30 minutes longer. Discard the bay leaf.
Sprinkle with the scallion tops and parsley. Serve in shallow soup bowls, and pass the rice and filé powder.