Yard Machine MTD Deck Drive?

I have a 2006 Yard Machine model 13AC762F729. It was given to me by a friend. From what she told me, the deck drive belt blew apart last time she used it. After looking at the deck diagram, buying a spring that was broken (part number 732-04280B) and replacing the "V" belt (belt number 754-04082), I can't get the belt tensioner to keep the belt tight. The blade will spin will get bogged down when it hits grass. I double checked that I had the correct belt, since the belt seems too big. It is missing the part 48 783-04602 Belt cover. I wouldn't think this would have an effect.

Is there a way to tighten the belt up, assuming this is the correct belt