Place ribs in a shallow pan. For marinade, mix together vinegar, Worcestershire sauce, 1/3 cup lemon juice, spice mix, and cayenne, then pour over ribs, turning to coat well. Cover and refrigerate ribs for at least 2 hours or as long as overnight.

Preheat oven to 200°. Pour off excess marinade from pan and discard. Cook ribs in oven for 3 hours.

For sauce, mix together ketchup, butter, vinegar, brown sugar, Worcestershire sauce, 1/2 cup lemon juice, mustard, and cayenne with 3/4 cup water in a saucepan. Cook over medium heat, stirring occasionally, until sauce thickens, about 15 minutes.

To finish ribs on a charcoal or gas grill, place on a rack over a low fire. Cook, turning once, until lightly browned and crusted. This could take 5 - 30 minutes per side, depending on hotness of fire, distance of ribs from heat, and type of grill. When ribs have browned, baste with sauce and cook, turning once, for 5 minutes more per side. Serve ribs with additional sauce on the side.