/6 headers

The best thing that anyone could do would be to send one of these exhaust manifolds directly to Doug Dutra.

He is, after all, the absolute guru of the slant six. He will test it and document the actual results and give you an honest, non-biased opinion. (even if he does manufacture his own system)

By the way, his Dutra Dual system when made from a feather duster exhaust manifold is quite impressive. It scavenges better because the feather duster exhaust manifold ports are larger than the normal slant six manifold.