You're absolutely right on the Pro Comp heads. I suspect two things helped them a bit here. First Dr. J's extensive porting and the fact that the engine ended up with forced induction. With the porting they were probably not much cheaper than the CHI's out of the box.
Several guys are making really good power with that block stroked to the 438 to 454 range and using the AFR 225 heads. I understand that setup allows a wider range of intakes as well.
PANTERA INTERNATIONAL
A DE TOMASO CAR CLUB
Presents the De Tomaso Forums
The On-Line Meeting Place for De Tomaso Owners and Enthusiasts From Around the World
Clicking on the banner will take you to the sponsor's website.