The Bolt 5/16-24x3/4" is the most widely applied product in the V8 5.7 YEMS 1990 ENGINE BELTS - PULLEYS ( four times ).
Some items from this specific schematic: Belt,crank/pwr. St, Washer,lkextrn7/16, Washer,lk Med 3/8", Washer,lk Med 3/8".
The lowest price component in this Belts - Pulleys parts-list fiche is the Wshr,flt,sae7/16".