part numbers/casting numbers for 1968 L36

[70CitrusZ]

Hi,
I don't know..are they?
I just thought from my engine build stamp of dec 23 1967,dec 5 or 13 would be too close to be installed..ie: 10 days after casting, but I don't know this to be fact.
My heads are cast sept/oct 67 and my intake is oct 67, so I just figured the exhaust manifolds should be similar, but maybe I'm wrong? I don't have my block nearby but I think it was Nov or Oct?.. If anyone else has any input That is why I posted this to start with, to see if the date ranges are correct on the parts I still require.
Mark.