Make the stuffing: Heat 4 tbsp. butter in a 12" skillet, over medium-high heat. Add beef; cook, stirring, until well-browned, about 10 minutes. Finely chop half the garlic, 5 ribs celery, and 3 carrots, and add to skillet along with scallions; cook, stirring, until vegetables are soft, about 25 minutes. Transfer to a bowl; add beets, olives, corn, and cilantro. Season with salt and pepper; transfer to a 9" x 13" baking dish. Refrigerate until ready to use.
Make the chile sauce: Place both chiles in a bowl; cover with boiling water, and let sit until softened, about 10 minutes. Drain, reserving 2 cups soaking liquid, and transfer chiles to a blender with remaining garlic, cumin, cloves, crackers, and 2 cups soaking liquid. Puree until smooth; set aside.
Heat oven to 450°. Arrange neck and giblets on the bottom of a large roasting pan; place turkey, breast side up, in pan. Season with salt and pepper and rub with remaining butter; roast until skin is golden brown, about 1 hour. Reduce oven temperature to 350°, pour chile sauce over turkey, and cook, basting every 30 minutes, until an instant-read thermometer inserted into the thighs reads 165°, about 2 hours. Transfer turkey to a cutting board; set aside. Pour pan drippings through a fine strainer into a bowl; discard solids. Meanwhile, place stuffing in oven; cook until golden browned on top, about 30 minutes; set aside.
Meanwhile, make the gravy: Return 1 cup fat from the drippings to pan and place over two burners of the stove; heat over medium-high heat. Roughly chop remaining celery and carrots, and add to skillet along with onion; cook, stirring, until soft, about 15 minutes. Add flour; cook, stirring, until smooth, about 3 minutes. Add stock; boil. Reduce heat to medium; cook, stirring, until gravy thickens, about 15 minutes. Pour through a fine strainer into a serving bowl, and season with salt and pepper. Serve turkey with stuffing and gravy on the side.