Put the beans in a large bowl or pot with water to cover and soak at room temperature overnight.
The next day, dice half the salt pork and leave the other half in 1 piece. Drain the beans and put them in a large Dutch oven with the whole piece of salt pork and enough water to cover, about 1 quart. Bring to a boil over medium heat, cover, and simmer until soft, about 1 1/2 hours. Drain the beans, reserving 2 cups cooking liquid.
Preheat the oven to 325 degrees F. Put the diced salt pork in another large Dutch oven (or clean the first one) and cook over medium-high heat, stirring occasionally, until translucent and slightly crispy, 3 to 5 minutes. Add the onion, molasses, ketchup, dry mustard, cooked beans and enough of the reserved cooking liquid to cover the beans. If necessary, add more water to cover the beans.
Bake, covered, until the beans are soft to the tooth and most of the liquid has been absorbed, about 2 hours. When finished, season with some salt and pepper and serve hot.