BigSmoker, I think that 8 hours on the ribs might be a little long. Even when I load up the smoker, ribs rarely take more than 4 hours. When I position the food on the racks I make sure there is room for heat/smoke to rise around & get the stuff on the higher racks.
Copper, I would put the raw ribs below the partially cooked brisket at first to keep cross-contamination to a minimum. After 2 hours or so, rotate them to the top and get the brisket back down lower.