[Excaliber]

The heads WERE pressure tested! This sounds kind of like plugging one hole only to find another, and another. Perhaps the heads were 'stage 3' ported, leaving the wall thickness a tad to thin? Shelby only offers Stage 2 porting. What ever the heck Stage 2 and Stage 3 means!

Both Edelbrock and Shelby are made from the same material and hardness spec. A quick comparison indicates they are virtually the same in all critical deminsions (wall thickness, chamber sizes, etc.). The Ebrock heads can be machined to accept larger valves. With larger valves they will ONLY fit the 427 original iron or Shelby alloy blocks (that applies to both manufacturers). The cost difference is profound, which leaves me wondering if the Shelby heads are really worth the extra dough?