Arrange the chickens, skin side down, on the grill over the drip pan. Cover and cook the chickens for about 1 hour at 250°, rotating them a few times, until the skin is crisp. Turn the chickens skin side up and continue to cook for about 1 1/2 hours longer, rotating them a few times, until an instant-read thermometer inserted in the inner thigh registers 165°. Monitor the grill throughout the smoking process and add more lit coals, soaked hardwood chips and water to the drip pan as needed to maintain the temperature and smoke level. Let the chickens rest for 10 minutes, then serve.