I helped a guy from work build a 383 sbc with this head http://www.jegs.com/p/AFR-Airflow-Research/AFR-Small-Block-Chevy-195cc-Eliminator-Street-Aluminum-Cylinder-Heads/2827547/10002/-1 , with the correct cam it made 522hp @6000 rpm with a rpm air gap and 750 hp holley.
It looks like 500hp is...