You can smoke prime rib and pork loin together in the smoker, but if you want them done at the same time you need to plan accordingly. Use a good meat thermometer to monitor the meat temperature while they smoke. The pork loin needs to reach 155 degrees internal to be done. Depending on how you prefer your prime rib, it needs to be remove at 125 degrees for medium rare, 130 for medium, and 135 for medium well. If one gets done before the other, place it in your oven on low to keep it warmed.