I know this isn't really what you're after, but I changed manifolds on my old 10:1 906 headed (unported) 440 w/ the MP 509/292 cam that ran high 11s w/ a Performer RPM intake and 830 holley.
I had an MP aluminum M1 dual plane manifold (aluminum version of the stock HP intake) that I put on just for the hell of it w/ the same 830 holley. I didn't take it to the track, but the loss of power was astonishing. It felt completely neutered and was all done at a lil over 5k rpm versus the 6200-6300 or so RPM the RPM intake would pull. Really wasn't expecting that drastic of a power loss on such a mild engine.
After that, I could definitely see why the 6 pack cars ran so much better than the 4V cars.