Lloyd, I've just added comparison photos to the thread at TC. I noted a difference in one area of the bases, one has a flat area (as does the base you pictured above) and the other has a circular indent. Now I am not sure what that means for the one with the indent (different supplier, service replacement, repro?) but I did note that Chuck Aleksinas has a 69 Z/28 air cleaner assembly for sale over at sYc and his also appears to have the circular indent. Interested in your thoughts and observations on this area.
Both lids have been rechromed in the past, so unfortunately neither still has the silk screening on the underside.