High flow exhaust Manifolds?

Does anybody make high flow exhaust manifolds for a bodies? I have headers, but am getting tired of the clearance issues I am having with them. I've smacked high spots in the road twice now and one pipe is almost collapsed. I'd love to go back to manifolds, but not the crappy flow!
Any help is appreciated! Thanks!

Original 318 manifolds will work just fine. Delete the flapper valve, ceramic coat them inside and outside, be done forever.

Header/manifold dyno test