Put the beans in a large pot with a tightly fitting lid and cover with cold water by 2 to 3 inches.  Bring the pot to a boil and let it boil, uncovered, for about 2 minutes.  Cover the pot and turn the heat off.  Let the beans soak for about 2 hours.

Taste a bean.  If it's tender (it won't be done), add a large pinch of salt and several grinds of black pepper.  Make sure the beans are covered with about an inch of water; add a little if necessary.  If the beans are still hard, don't add salt yet, and cover with about 2" water.  

Bring the pot to a boil, then adjust the heat so that the beans bubble gently.  Partially cover and cook, stirring infrequently, checking for tenderness, about 15 or 30 minutes.  

Preheat the oven to 300F.  

Cube or slice the salt pork or bacon, and put it in the bottom of a bean pot or other deep ovenproof pot with a lid, like a Dutch oven.  Drain the beans (reserve the cooking water), then mix them with the molasses and mustard.  Pour them over the meat.  Add enough boiling bean-cooking liquid (or water or both) to cover the beans by about an inch.

Bake, uncovered, checking and stirring after one hour, and every half hour after that, and adding more water if necessary.  After about 3 hours, taste and adjust the seasoning; you may add more salt, sweetener, or mustard.

When the beans are very tender, scoop the meat up from the bottom and lay it on top of the beans; raise the heat to 400F.  Cook until the pork browns a bit and the beans are very bubbly, about 10 minutes.  Repeat twice.  Serve hot.