From what I understand, it takes a significant amount of work (welding, grinding) on the gen3 single carb intakes to make them make power. I would start by contacting someone like Wilson manifolds for intake design/help.
I have a friend who’s just getting his porting business started so I figured I’d let him have his way with the heads and manifold.
Blackbird Performance builds ready to run 6.4s, and their 600hp version is mostly stock other than cam, ported heads and single plane manifold.