Do block huggers effect hp

Here's the Magnum on a different engine and test.
http://www.hotrod.com/how-to/engine/1406-comparing-headers-and-manifolds/

Don't get me wrong, I think you offer a good alternative for those that choose to run manifolds. I swapped out my 73 340 manifolds (which are the worst flowing of the 340 manifolds) and dropped in the Summit 1 5/8 headers everyone knocks and got a good bang for the buck hp wise.