there's pro's and con's to everything. when i did edelbrock rpms the castings and port window location wasn't great. the rocker geometry wasn't close so there was a push rod expense. i wanted to run factory valve covers and they wouldn't fit, another expense. pro's are spark plug selection and i do think they burn a little cleaner than factory iron. power wise i don't think they make any more power than a ported big valve iron head they replaced and definitely cost a little more to install in the long run. if all you have is '516's then you'll need to do something for heads. 11:1 with pump gas would make me edgy but you'll have to pick your poison.