I searched the Simplicity site and did not come up with an answer. A few years back I came up with the manual there for my mower. Guess you already tried that though. Any luck calling them?

(262) 377-5450 might be there phone number according to http://www.answers.com/topic/simplicity-manufacturing-inc

If that fails there is a "contact us" via email or snail mail. Of course the website says you should contact your local (rip-off) dealer.

Here is a link that might be useful: Simplicity Site

go to the store you bought the belt from some of them have the diagrams

To make it easier, you should drop the mowing deck. then raise the tractor and set it on jack-stands, or something that won't allow it to tip over, or fall on you. Clamp the brake/clutch pedal down tight.
Then lying on the ground, or the floor of the garage, slide under and look at the pulley layout. The Vee of the belt goes around the vee pulleys, and the flat back of the belt goes around the flat idler pulley. Look for belt guides that keep the belt on the pulleys. When you think it is on correctly, then allow the clutch/brake pedal to come back, then slide back under, and look for any place where the belt might be rubbing on a belt guide, or a part of the underside. If none of that, then if the belt is tight, when the clutch pedal is out to operating position, and none of the belt is rubbing on anything, you probably have it on correctly. Some lawn tractors have a sticker on the underside of the tractor step, which shows the correct belt routing. ATHOUGH!! It is also possible to get the belt wrong on some of the pulleys and still be tight, which could propel you thru yer mom's favorite petunia patch! Backwards!
I had a Broadmoor, but sold it. the new owner had to buy a new deck belt, which i gave him the number for, but he said it was too long. At that point, i went to his place and correctly routed the new belt, and all was good!