High flow exhaust Manifolds?

Yep 68-71 340 hi po manifolds. From what I understand these flow about as good as shortie headers. They are pricey nowadays and originals are in limited supply. As hemisedan stated theres repops of them out there if casting numbers and originality dont interest you. I dont believe the repops come with a heat riser flap or the holes drilled for one. The bosses are cast in for a heat riser however.