Combine the salt, pepper, allspice and mace; rub over the roast. In a small bowl, combine the tomato juice, onion, 6 tablespoons oil, lemon juice and vinegar.
Pour half of the marinade into a large resealable plastic bag; add roast. Seal bag and turn to coat; refrigerate for 8 hours or overnight. Cover and refrigerate remaining marinade.
Drain and discard marinade from meat. In a Dutch oven, brown roast on both sides in remaining oil over medium-high heat; drain. Pour reserved marinade over roast; add bay leaves. Bring to a boil. Reduce heat; cover and simmer for 2-3/4 hours or until meat is tender.
Remove roast and keep warm. Discard bay leaves. Skim fat from pan juices. In a small bowl, combine cornstarch and water until smooth; gradually stir into pan juices. Bring to a boil; cook and stir for 2 minutes or until thickened. Strain; serve with meat.