I run a 3.25" upper and a 8lb. lower with a 82.5" belt and 90mm aux + idlers. I have both 90mm & 100mm pulleys to get the correct length required to work. I beleive a 81.5" belt will work with the 3" upper. You can change the lower Metco idler also to get the correct length. I also ground off a little of the tenchner to get more play to put the belt on.