IIRC, date codes on hipo exhaust manifolds decode just the way they look. In your case it decodes to September 1st of, most likely, 1967. I suspect there should be a part number of C7ZE-9431-A or C7ZE-9430-A on the manifold as well. From what I remember, the date code was located on the flange side of the manifold. The part number was located on the opposite side. Hope this helps!