Simmer the pork neck bones and shrimp shells in 6 cups of water for 40 minutes, skimming foam. Strain and discard the solids.
Heat 1 tablespoon oil, sizzle the annatto seeds 30 seconds until the oil turns orange-red, then discard the seeds. Add shallot and garlic; cook 1 minute. Add the strained stock, fish sauce, sugar, and black pepper; simmer 10 minutes. Season boldly — the broth should taste intense.
Toss the sliced pork with turmeric, fish sauce, and black pepper. Sear in a hot skillet with a splash of oil until golden at the edges, 5–6 minutes. Set aside.
Sear the shrimp in the same skillet, about 2 minutes per side, until pink and curled. Remove from heat.
Heat 3 tablespoons neutral oil until shimmering and pour over the sliced scallion greens in a heatproof bowl to make scallion oil.
Boil the soaked noodles 4–6 minutes until tender with a bit of bounce. Drain, rinse briefly in cool water, and divide among 4 wide, shallow bowls.
Arrange pork and shrimp over the noodles. Ladle 1/2 to 3/4 cup of hot broth over each bowl — just enough to pool at the bottom. Spoon over scallion oil, scatter crushed peanuts, and add a handful of herbs. Serve immediately with toasted sesame rice crackers, lime wedges, and chilies.