[Tom Goldman]

I doubt the long runners are much bigger than 325cc on those heads.
I have a set of welded AFR's 074's on my 468 back up motor that flow somewhat better than a set of Dart Pro1's,but they are nowhere as strong or reliable. seats and guides dropping ,along with broken rocker bosses put most of these heads on the shelf years ago.
spend the money on a Dart or Brodix head.
something that is more properly sized for a 500" motor.