Well whit, I have the same problem. I have a Craftsman lawn tractor Model no. 917.270780. I just purchased a new deck belt (to engage blades) at Sears yesterday ($22.99 + tax).
Yes, The belt routing diagram is under the left foot brake, right on top of the deck itself.
I'm going out to attempt to install it, now. I wish there was a way to find out the correct procedure to install it. I have no manual.
My grass is as high as an elephant's eye!
John Porcello, September 2006