8. The Hesco head actually does have its own EO number and is registered with the California Air Resource Board to be smog-legal on both the Jeep 4.0L engine and the older 4.2L engine. The valves are all stock-sized, and the head actually greatly improves emissions when adapted to the 4.2L engine. It comes with high-performance springs, hardened seats and silicone bronze guides. You can use either stock rockers or put roller rockers on the Hesco head.