Sort and wash beans; place in a large Dutch oven. Cover with water 2 inches above beans; let soak overnight. Drain beans.
Combine beans, salt pork, and water to cover in Dutch oven. Bring to a boil. Reduce heat; cover, and simmer 30 minutes. Drain beans, and slice salt pork.
Place salt pork in bottom of a 3-quart casserole; stir in beans, molasses, and mustard. Add water; cover and bake at 350° for 2 hours. Uncover; bake for 45 minutes or until beans are tender and lightly browned.