Rinse beans and pick over to remove any stones or damaged beans. Place in a 6-quart Dutch oven. Add 8 cups water; cover and soak 8 to 24 hours. Sprinkle chicken generously with salt and pepper. Refrigerate, uncovered, preferably overnight.
Drain and rinse beans; return to pan and set aside. In a large nonstick skillet, slowly cook salt pork until lightly browned. Add to beans along with whole pasilla peppers and the 8 cups stock. Add a big pinch of salt; bring to a simmer. Skim as needed. Simmer, partially covered, for 1-1/4 hours.
Meanwhile in the skillet used to cook the salt pork, slowly cook the chicken, skin side down first, until very well browned about 15 minutes. Remove chicken from skillet and set aside. Pour off all but 2 tablespoons of fat from pan. Add onions and a good sprinkle of kosher salt. Stir well, scraping up any browned bits from the bottom of the pan.
Add peppers and garlic; stir well. Cook slowly for 5 to 10 minutes, stirring often. Sprinkle with paprika, chili powder, and cocoa; stir well. Stir in the tomato paste and honey. Cook another 3 to 5 minutes.
If liquid level is below the beans, add more chicken stock or water. Ladle a cup of the bean liquid into the onion-pepper mixture. Bring to a simmer; carefully transfer to Dutch oven with beans. Taste for seasonings and adjust as needed.
Add chicken thighs and cook, partially covered, at a low simmer for 10 to 15 minutes.
Add the pumpkin and cook until chicken is tender and pumpkin is cooked through but not collapsing, about 15 minutes. Remove and discard salt pork and pasilla peppers. Serve over rice with cilantro, red onion, sliced peppers, and sour cream.