Combine first 5 ingredients, and, if desired, sugar in a large bowl. Stir together 2 eggs and buttermilk; add egg mixture to dry ingredients, stirring just until moistened.
Heat bacon drippings in a 10-inch cast-iron skillet or 9-inch round cakepan in a 425° oven 5 minutes. Stir hot drippings into batter. Pour batter into hot skillet.
Bake at 425° for 25 minutes or until golden; cool and crumble. Freeze in a large heavy-duty zip-top plastic bag up to 1 month, if desired. Thaw in refrigerator.
Melt butter in a large skillet over medium heat; add green onions and celery, and sauté until tender.
Stir together remaining 4 eggs in a large bowl; stir in cornbread, onion mixture, stuffing mix, and broth until blended.
Spoon dressing into 1 lightly greased 13- x 9-inch baking dish and 1 lightly greased 9-inch square baking dish. (Cover and freeze up to 3 months, if desired; thaw in refrigerator 8 hours.)
Bake 13- x 9-inch dish, uncovered, at 350° for 1 hour or until lightly browned. Bake 9-inch square baking dish, uncovered, 50 minutes or until lightly browned.