Don't remember that test.
I have issues with the magazine test, not because they could be skewed by sponsors, but because the 300 HP crate motor is too tame to really show a difference. Any motor that get's swapped from the beer barrel intake and EFI to a dual plane with a 4 bbl and sees virtually no difference in power between the two is not going to exercise the 318 manifolds let along anything bigger than that.
I did find a 440 that Jim did (now that I know his screen name) where he put BB HP manifolds on a low compression 440 build and saw almost no power difference when compared to the standard BB manifolds. Is that the one you are referring too?