340 exhaust manifolds

68-70 340 are the better manifolds. 71 -74 340 360 have a different pass. side, early pass. side has a better flow..318 has totally different in inside diameter and not recomended for 340 360. I would only use the early manifolds if I was going to go to any. Manifolds do not flow near as good as equal length headers. I am going make a set of stainless headers for mine to prevent rust out , although I have seen that ceramic coated headers are really durable on cars we have worked on.