Boil crabs for 20 mins. in lightly salted water. Remove, save water. Put 2 Tbsp. of oil and 1 of butter in a non-cast iron skillet and fry Okra until all traces of sliminess disappear. In a deep pot, put remaining oil, stir in flour, make dark brown roux. Add onions, garlic, green peppers and celery to roux, stir for 5 min. Add diced ham and cook for 10 min. on low heat. Stir in tomatoes, shrimp and simmer.
In 8 cups of crab water, boil the shrimp heads, peelings for 15 mins. Add the Okra to the large pot, stir for a few minutes then strain the shrimp water to the mixture. Add the remaining seasonings and simmer slowly for 2 hours. Remove the back shell, belly flap, legs and claws from the crabs. Clean out all unwanted material from the crabs, break crabs in half and lightly crack the claws. Add crab halves & claws to the pot. Cook another 15 mins. adding the green onions during the last 5. Serve over rice. If File' is desired, sprinkle over rice prior to adding the gumbo.