The 340's do flow better than any of the truck manifolds for sure but so do the Magnum manifolds. Actually the best manifold combo is the drivers side 340 manifold and the passenger side Magnum manifold. The 340 manifolds on both sides exit in between cyl#'s 5 and 7 and 6 and 8, so they are in between the Magnum manifolds and the 318/360 manifolds. Why not just get some shorty block hugger headers from Summit?
Exhaust on a Mopar 300hp Crate Engine - Tech Articles - Mopar Muscle Magazine
Read the tech article on installing an Exhaust on a Mopar 300hp Crate Engine, brought to you by the experts at Mopar Muscle Magazine.