Place eggs in a small saucepan and cover with cold water by 1-inch. Bring to a boil. Turn off heat; let stand, covered for 13 minutes. Drain, cover with cold water, and let stand, covered for 2 minutes. Peel, and quarter eggs, cover and refrigerate.
Fill a large bowl with warm water. Add noodles and let soak for 25 minutes, stirring to separate as they soften. Drain.
Heat oil in a large, heavy stock pot over medium-high heat. Season chicken and shrimp with salt and pepper. Working in batches, cook chicken turning occasionally, until browned on all sides, about 5 minutes. Transfer chicken to a plate. Add shrimp to the stockpot, and cook stirring until bright pink, 2-3 minutes. Transfer shrimp to another plate.
Reduce heat to medium. Add additional oil if necessary. Add onion, carrot and garlic and cook, stirring occasionally, until tender, about 4 minutes. Add pork and cook breaking up with a spoon, until no longer pink, about 3 minutes. Stir in fish sauce and cook 1 minute.
Add cabbage, and toss to coat. Add noodles, chicken and stock, and gently stir. Bring to a boil. Reduce heat, cover and simmer, stirring occasionally, until noodles are tender and most of the stock has been absorbed, about 10 minutes. Remove form heat, and let stand, partially covered, 5 minutes. Add shrimp and lemon juice, gently stirring to avoid breaking noodles.
Transfer to a platter. Sprinkle with scallions. Arrange hard-boiled eggs around noodles and serve warm or at room temperature.
SHRIMP STOCK: Heat oil in a saucepan over medium heat. Add onion and garlic, and cook until softened, about 4 minutes.
Add shrimp shells, bay leaf, and red pepper flakes, and cook, stirring until shells are bright pink, about 1 minute.
Add fish sauce, and cook for 1 minute. Stir in chicken stock and water. Raise heat to medium-high, and bring to a boil. Reduce heat and simmer, partially covered for 20 minutes.
Pour through a sieve; discard solids. Stock can be stored in an airtight container in refrigerator for up to 3 days or in the freezer for up to 1 month. Makes about 2 1/2 cups.