Pat all meat dry. Mix mustard and spices for the spit roast. Spread the smoked pork loin all around and place on the bone. Season high rib with salt and pepper. Place both roasts on the prepared grill and cook over indirect heat with closed lid for approx. 2 hours.
Remove both roasts from the grill, wrap them boneless in aluminium foil and let them rest for about 10 minutes. Cut them open.