422 dyno fail

Something is fishy. About 15 years ago, Mopar Muscle took a bone stock 340 and added a Comp 268 Xtreme energy cam/springs and lifter kit, 850 CFM carb, Edelbrock Air Gap, 1 5/8" headers and it made 392 HP (a little over 1.1 HP per CI). I followed that same recipe on my motor. There was no fancy head work, no manifold port matching, etc. With the specs listed, the Op's motor (at 422 CID) should have made around 460 HP. A bigger carb should have put it up to over 475. With that combo I see no reason why one HP per CI was not achieved. Like I said, something is fishy.