the screen is there to stabalize the air coming in. its suposed to prevent turbulance inside the manifold and i know for a fact that you should never take off that screen. now the manifold also has runners inside that guide the air flow into the heads. perhaps the two need eachother but with a ported manifold and those runners shaved off you dont get the turbulance anymore.
The guy that tunned the car is the authority in LSx tunning. if he says its cool then its cool.