Dave I ran 516 heads last summer on a 426. I did put in the 1.74 exhaust valve and bowl cleanup. Was able to get 11.90 in a light car. I was just "killin time" till my new motor was ready. If there ready to run and all the budget will alow run em till you can get something better. If you have to spend any thing much at all on them I'd jump right to an Alum. head.