Belts are belts- - - -they're not some exotic item that will cause the truck to self-destruct if a slightly out of spec one is used. As long as the fan, water pump, and charging system works, who cares if a tiny fraction of an inch of width is different? A belt 11 MM (7/16") wide will work on either a 3/8" or a 1/2" pulley with a minimum of hassle. Getting anal-retentive about details might be fine for a truck that's shooting for a 100-point score at a concours car show. Otherwise, shouldn't a little bit of common sense be applied?
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!