Look at the torque curve in the
Power and Performance News write up.
It starts nosing over in a hurry at 4500 rpm and manages to drop to 480 by 6400 rpm. This is not the kind of performance you would expect from a high flowing $5K set of custom heads. Even worse the torque decline shows no sign of letting up at 6400 but instead is headed south at an increasing clip and so is the HP.
A declining torque curve is the hall mark of poor volumetric efficiency. From a visual inspection of the photos you would not expect this. The dyno results tend to be the real thing however and they tell a very different story.
A 427 inch motor that only makes 600 HP is yesterday's news. A modest build using something like the old tunnel port heads with today's cams would easily crest 700 maybe 750 HP and still be a reasonably good driving street engine.
$5K is a lot of money for eye candy — and that is just the price of the heads. I am going to assume cam pricing would be a push. That still leaves custom intake, pistons, and exhaust that you have to step up for.
All in all there are better solutions available.
Ed