Here's another tip for you . . . look for 72-74(I think), Road Runner small block (318) exhaust manifolds . . . you can see how they are stamped on the manifold - port sizes are the larger 340/360 head, and the right side manifold was never drilled for heat riser. Also I think the outlet port size is larger than standard 318 . . . yet the manifolds LOOK like standard 318 !! Gotta love the small things . . .