Remove giblets and neck from turkey; discard. Rinse turkey thoroughly with cold water; pat dry. Combine orange juice, water, 1/2 cup bourbon, and molasses in a 2-gallon heavy-duty zip-top plastic bag; add turkey. Seal and marinate in refrigerator 4 to 24 hours, turning bag occasionally. Remove turkey from bag, reserving marinade.
Preheat oven to 350°.
Tie ends of legs with cord. Lift wing tips up and over back, and tuck under bird. Sprinkle 1/2 teaspoon salt into body cavity. Stuff cavity with oranges. Place turkey on a broiler pan coated with cooking spray or on a rack set in a shallow roasting pan. Insert meat thermometer into meaty part of thigh, making sure not to touch bone. Bake at 350° for 3 hours or until thermometer registers 180°. (Cover turkey loosely with foil if it gets too brown.) Remove turkey from oven. Cover turkey loosely with foil; let stand at least 10 minutes before carving. Discard oranges.
Pour reserved marinade into a saucepan; bring to a boil. Skim foam from mixture with a slotted spoon; discard. Reduce heat to medium; cook until reduced to 3 1/2 cups (about 15 minutes). Combine 1/4 cup bourbon and flour in a small bowl, stirring well with a whisk. Add to reduced marinade; bring to a boil, and cook 1 minute, stirring constantly. Stir in 1/4 teaspoon salt. Serve sauce with turkey. Garnish with orange slices and parsley sprigs, if desired.
NOTE: To substitute a 5-pound turkey breast for a 12-pound turkey: Omit the 4 peeled oranges used to stuff the whole turkey; disregard the giblets, neck, legs, and wings. Insert meat thermometer into meaty part of turkey breast, making sure not to touch the breastbone. Bake at 350° for 1 hour and 45 minutes or until thermometer registers 170°. (Cover turkey loosely with foil if it gets too brown.)