Make chicken stock for the ramen. Rinse chicken bones and place them in a large pot covered with water. Bring to a boil over high heat and continue to simmer for 10 minutes. Remove from heat and drain, rinsing bones and pot. Place chicken bones back in the pot with 8 cups of water, ginger, garlic, and 3 stalks of green onion. Cover the pot, bring to a boil, reduce heat to low, and simmer for 2 hours. Skim fat and keep warm.
Meanwhile, make chashu pork. Combine pork belly with sake, soy sauce, mirin, water, sugar, ginger, garlic, and the stalk of green onion. Cover the pot and bring to a boil. Reduce heat to low and continue to simmer for 2 hours or until pork is fall-apart tender.
Make tare. Combine all ingredients for tare in a small saucepot and bring to a boil over medium heat. Reduce heat to low and simmer for 5 minutes. Strain, discarding ingredients. Let cool.
Assemble ramen. Cook noodles and drain. Pour 1 tablespoon tare, 2 cups chicken broth, and 1 teaspoon MSG per bowl. Add noodles, thinly shaved onion, radish sprouts, scallions, and a boiled egg. Serve immediately.