Howdy BDPony:
And Welcome to THE Forum. Yes, it is that good. First off I'm curious how and where you manifold broke.
My favorite is a C8 casting because it is a bit beefier than earlier castings and it is less encumbered with extra bungs and taps for EPA type crutches. I have no personal experiences with the after market manifolds and like you have heard various experiences.
Was you manifold an OEM and never off the OEM head, or has it been off when the head was rebuilt? Was it re-installed using an aftermarket exhaust manifold gasket? FYI, '67 engines came from the factory attached to the head with no gasket at all.
Sorry, not much help here.
Adios, David