I believe Shadow's setup to create the power and performance it does due to the precise tuning he does.
Everything in his system is set up to run with that ported stocker.
So yes, you CAN make great power with a ported stock mani,
but why would you when there are great headers to be had that require no finessing?
Understandably, the ported mani will be much less expensive, but will never out flow a header.
Shadow's Charger, IMHO, is an anomaly.
NON-CB and a ported stock exhaust mani.
I'm not sure there's ever been another to do what he's done with these parts.
Personally, and even though his pressure differential is surely 1:1,
I'd LOVE to see what the improvements would be for him with a header installed,
and tuning altered slightly to accept one.
(And would like to see him add an alcohol injection system as well. lol)