Rebuilt 1967 single 3904391 head, head has stock 2.19/1.72 valves and it unported. Month was not cast into the cylinder head, it is cast 20-6. Searching the internet the only month in 1966 that a #391 head was cast was I or September. Head has had 1 valve cover bolt removed at some time and the top couple threads aren't the best, the rest are good and a valve cover bolt fits snug when tightened down. $900 plus shipping, head is located in SE Michigan