Combine flour, thyme, parsley and pepper; rub over outside of roast.
Place roast with rib ends down in a large roasting pan. Bake at 325° for 2 hours.
Meanwhile, in a skillet, saute onion in oil until tender. Add mushrooms, broccoli, salt, bouillon, thyme and pepper; cook for 8 minutes or until broccoli is crisp-tender.
Stir in stuffing mix and water. Turn roast over with rib ends up; fill center of roast with about 3 cups stuffing.
Bake 1 hour longer or until meat thermometer inserted into meat between ribs reads 160°.
Bake remaining stuffing in a greased covered baking dish during the last 40 minutes of baking time.
Transfer roast to serving platter; let stand 15 minutes before slicing. For gravy, drain drippings into a measuring cup; skim and discard fat. Add enough water to drippings to measure 3 cups; stir in flour.
Pour into skillet, stirring to loosen browned bits. Add salt and pepper. Bring to a boil over medium heat; boil for 2 minutes, stirring constantly.