Origins of a 9E1-AF cylinder head

[Scarlet O'Hara]

Here's another one for you Chris, I did't think they were that uncommon and just assumed that they all had the patent number. This one's on the Type 65 and most of the other sports parts on the car have a 9E number apart from the torque tube socket that is 9C144. The much later Speedy crankcase (M248719) has a 9E199 number. Did the 9E numbers possibly come in with the change to the long chassis but left over 9C parts that could be fitted got went onto early 65's and 75's?    
Forgot to say so hence a quick edit. The head isn't wedge shaped and is the same thickness all over, it also has 18mm plugs.