Also pay attention to where the
oil returns into the valley. Hold an intake manifold gasket set up against the head and you'll see that the return area is partially blocked by the manifold gasket. You can improve drainback in this area up by creating a channel along the (manifold side) face of the head. You can post a question over on
332-428 Ford FE Engine Forum and someone will undoubtedly post some pictures for you.
Chris