Buick Nail Head? Vintage cast iron V8 and similar items

Can anyone identify these? Buick nail head?, Rover? Seems to be an important set of vintage V8 exhaust manifolds, old style, cast iron, somewhat lightly used. Since I can't find a matching image after exhaustive googling I assume they are rare casting numbers F2400 CB and F 2409 CC. The closest look seems to be the Buick Nail Head but the spacing does not appear to match. Might be the 1st Nail Head? 1963? The connection for the exhaust pipe is threaded as shown in the photo. Port diameter is about 1 5/16", 3 1/2 cm I guess that is the early lower cubic inch engines. Maybe the Rover version? Very unusual exhaust port pattern with a big gape between the middle cylinders. They are from the same vintage exotic car parts collection I have listed on this and other sites but I can't identify the mfg'er for these. Please help so I can set the appropriate price. These things need to find the engine they belong to. I did some googling of exhaust manifold images for Packard, Cord, Bentley, Rolls Royce, Delahaye, Alfa, Studebaker, Duesenberg, Ford, GM, Pontiac, Buick, Cadillac. Did not see these exactly yet. Please check our other listings including Fire Alarm Equipement, Vintage Automotive Parts, manuals, literature, badges, pins, etc.