I was a little mystified to see this head on another forum, and then 'corrected' to be an R12/136

https://www.nortonownersclub.org/no...6579/689392924/1956-58-cylinder-head-jpg

With only 4 fins below the spark plug.
I ask you.... ??

Anyone want to have stab at what it really is.
Prove you know more than the 'eggspurts'...