Preheat the oven to 350 degrees F. In a pot, add the giblets, neck bone, onion and stock. Simmer and cook on low for 20 minutes. Discard the onion and neck bone. Remove the remaining giblets and chop. Place back in the stock and set aside. Strain the oysters over the pot of stock and set aside the oysters.
In a large bowl, mix all the stuffing cubes with the parsley and set aside.
In a saute pan on medium heat, add 2 tablespoons butter, celery, onions, sage, thyme and garlic. Season with a pinch of salt and a nice grind of pepper. Cook until the onions and celery are tender, but the garlic is not browned. Remove to the bowl of bread cubes. In the same pan, add the remaining 2 tablespoons butter and the oysters. Saute until the edges begin to curl on the oysters. Remove to the bowl of stuffing cubes and stir to combine with everything. Pour the stock over the mixture and stir. This is a wet dressing, so it will be very moist. Pour into a 13-by-9-inch baking dish. Press down to make it compact, and then cover tightly with aluminum foil. Bake for 45 minutes, then raise the temperature to 400 degrees F and bake uncovered until golden brown on top, about 15 minutes more.