Am I missing something important?
The Modman looks very much like the original 1958 350" (and 383/343 hp) B 2 X 4 divided single plane iron manifold, or the Offy "360 degree", with the center divider removed.
I make some comparos on my site here: http://victorylibrary.com/mopar/intake-tech-c.htm

The closed off angle piece as both a volume reduction and a flow enhancement is brilliant! I have a feeling that the sharp top edge may "trip" mixture trying to swap left & right sides. Perhaps capping the angle with a half-round of 3/4" tube may help?