Thaw shrimp, if frozen. Peel and devein shrimp; rinse with cold water and pat dry with paper towels. Coarsely chop shrimp and set aside. Meanwhile, cook pasta according to package directions; drain. Rinse with cold water; drain again.
Preheat oven to 350°F. In a large nonstick skillet cook sweet pepper and onion in hot oil over medium heat for 5 minutes, stirring occasionally. Add shrimp. Cook for 2 to 3 minutes more or until shrimp are opaque, stirring occasionally. Transfer shrimp mixture to a bowl.
For sauce, add garlic to the same skillet. Cook and stir for 30 seconds. Remove skillet from heat. Carefully add wine; return skillet to heat and cook for 1 to 2 minutes or until most of the wine is evaporated, stirring to scrape up browned bits from bottom of skillet. In a small bowl whisk together ¾ cup broth and flour. Add all at once to the skillet along with the milk. Cook and stir until thickened and bubbly.
Stir ⅔ cup of the sauce and the crab into the shrimp mixture. Spoon shrimp mixture evenly into the cooked shells and arrange shells in a 2-quart square baking dish. Pour remaining sauce over the shells.
Cover and bake for 30 to 35 minutes or until heated through. Let stand for 10 minutes. Sprinkle with basil and chives just before serving. Serve in shallow bowls.