p600 in 86' mustang have belt problems

Dear Friends...well here I am again looking for some advice.
I have the P600 intalled into my 86 mustang, i have the old belt tensioner ( not spring loaded) for the P600. I do have some serious problemas with it, I already destroyed 3 belts so far, I looked my pulleys and one was out of aligment , the supercharger is to far to the front side of the car, so I am going to align the blower and see if this is the problem.
But I saw on some of the ATI brochures that the tensioner is placed at the below side of the belt, I mean not like on the grooves but on the flat side of the belt but to the one that its down the supercharger...I hope you get my idea..
But some other pictures I looked they show the tensioner in the upper side of the belt.
So on what side goes the tensioner? on the upper part of the belt near the supercharger or the down side of the belt near the supercharger?
BTW..I have the 8 rib belt and pulleys, and my car wont go over 6000 rpm...i pussy shift at 5,800 rpm most at the time.
Thanks for the help guys...any idea or suggestion is welcome.
Pablo
:(