Rinse bones and beef three times, then transfer to a large pot. Add 6 cups water and heat over medium-high heat. Bring to a bare simmer, then remove from heat. Drain and discard water, then gently rinse bones and meat.
Return pot with bones and beef to medium-high heat and add 3 quarts water. Add radish, scallions, cinnamon, ginger, star anise pods, bay leaves, cardamom pods, peppercorns, salt, cumin seeds, fennel seeds, granulated sugar, and white pepper. Bring to a simmer, reduce heat to low, and partially cover. Continue to simmer until meat is fork-tender, about 2 hours.
Transfer beef and radish to a heatproof container. Let cool to room temperature, then refrigerate. Thinly slice beef and radish once completely chilled.
Keeping bones and spices in pot, continue to simmer 2 more hours. Remove from heat and stir in 2 cups water and MSG, if using. Strain and reserve broth, discarding bones and spices.
In a large pot of boiling water, cook noodles until al dente, 4 to 5 minutes. Drain and transfer to a serving bowl.
Top with broth, a few slices of beef and radish, egg, if using, chili oil, scallions, and cilantro.
Transfer any remaining broth to clean glass jars and refrigerate for up to 10 days.