If you see centerbolt valve covers like this and there’s “5.7L” stamped on the rear of the block, pop the valve cover off and check the head casting numbers. The ’96-’99 350s received GM’s excellent Vortec iron heads. Based off GM’s LT-1 Corvette heads, the 170cc ports and 1.94-inch intake/1.50-inch exhaust valves will support big power. Look for PN 12558062 or PN 10239906. Despite some internet claims, the centerbolt heads on the 305s aren’t true Vortec castings and have smaller valves and ports.