Clean crabs, discarding spongy substance in main shell. Reserve claws and other meaty portions. Clean shrimp, reserving shells. Place shrimp shells in deep saucepan with water to cover generously and simmer 30 minutes or longer to make broth. Pour oil into heavy skillet to depth of 1/8 inch. Heat and add beef, ham, sausage, gizzards and salt pork. Saute until lightly browned, stirring occasionally. Pour meat mixture into large kettle and add 1 can tomatoes and enough strained shrimp broth to cover generously. Add bay leaves, cover and simmer about 30 minutes. Heat 2 tablespoons more oil in skillet and add onions, green peppers, celery and garlic. Saute until lightly browned, stirring now and then. Add vegetable mixture and chicken parts to kettle and simmer 30 minutes longer. Heat 2 tablespoons oil in another heavy skillet, add okra and cook, stirring often, until lightly browned and loses stickiness, about 30 minutes. Add shrimp to okra and saute 3 or 4 minutes longer, or until shrimp turns pink. Stir in 2 tablespoons sugar. Add okra mixture to kettle. Drain second can of tomatoes, reserving liquid. Add tomatoes, crab and enough tomato liquid and water from shrimp shells to keep mixture in kettle soupy. Simmer about 30 minutes. Add parsley flakes and remaining 2 tablespoons sugar. Season to taste with salt and pepper. Serve at once or refrigerate and reheat later. Serve over hot rice in deep soup bowls. Pass hot pepper sauce and crackers with gumbo, if desired.