For the early V10 years (i.e. 1999, 2000) some catalogs don't list the F53, so be careful. Some parts will be identical with F550 super duty..
ALSO - Check Rock Auto - Their listings for the F53 are reasonably accurate. Pay attention to your chassis gross weight, sometimes parts for the lighter chassis are different than the heavy chassis
SERPENTINE BELT - I'd replace the belt and keep the old one as a spare. That way you know its the correct one and it fits. The belt should be approx 110 inches.
1999 Fleetwood Southwind 35S (Ford F53 6.8L V10 275hp 4R100 4 spd trans) - Toad 2003 Saturn Vue.
It won't do MACH 2, but I can get a sandwich and take a pee.