Place the sausage in a large bowl and mix in the chestnuts, green onion, 1/2 cup of soy sauce, eggs, garlic powder, and breadcrumbs. Roll the mixture into 1 to 1 1/2 inch balls and place on a broiler pan. Bake in the oven for 1 hour. When done, place the meatballs in a slow cooker.
While meatballs are cooking, prepare the sweet and sour sauce by stirring together the sugar and cornstarch in a large saucepan. Pour in vinegar, pineapple juice, ketchup, and soy sauce to taste. Bring to a boil over medium-high heat, then reduce heat to low, and simmer until thickened. Pour sauce over meatballs, and keep warm in the slow cooker.