It's a specific application, the long runners of th stock manifold give you low end Torque, for the stump pulling a truck is supposed to do.
What I'm doing doesn't require it, Short runners, or more of a Plenum is for High end Horsepower. It is a desired type of intake for a Turbo application.

I Cut the runners out with a Sawsall, The guy who did my head work had the flange welded back to the tank and then matched all the port sizes.

Thank you.