Set the rack of rib bones in a large roasting pan, meaty side up, and season with salt and pepper. Set the pork loin on the rack, fat side down. Add the 6 peeled garlic cloves to the pan and pour in 2 cups of water. Roast the pork for 30 minutes. Add 1 cup of water to the pan and roast the meat for 30 minutes longer. Turn the pork loin fat side up and roast for about 30 minutes longer, or until an instant-read thermometer inserted in the thickest part of the meat registers 145°. Transfer the pork to a carving board and cover loosely with foil for at least 10 minutes or up to 20 minutes.