Mine is a 2004 but I think the belt is the same. here are the numbers for different brands.
Serpetine Belt number Workhorse W0000581
Auto Zone Kelley Spring 1080K6
Gates K061080 or 25-061080
AC Delco 6K1080
Napa 25-061080
Carquest K061080
Goodyear 4061080
If you can't find a belt routing diagram somewhere on the engine, I could not find one, make sure you draw one before taking the old belt off. take digital pictures also, might help. A 3/8" drive ratchet or breaker bar inserted into the square hole on the side of the tensioner works fine to release the tension to remove the belt
Belt diagram
Othertonka
2004 Southwind 32VS 8.1 Workhorse chassis
2002 CRV Toad
U. S. Gear Unified brake system
Retired Fire Captain, SFD