I don't know much about Knuckelheads so please look at the pictures for information. I think this is a rear head for a 1940-47 motor. I also believe it is a large port. I see others make a note to mention the condition of the exhaust port. This EXHAUST PORT is NOT cracked. Don't do Krack. There don't seem to be any combustion chamber damage. There seems to be one small fin broken near the spark plug hole. It is dirty and rusty. One valve guide has been removed and one remains. The intake manifold nut is still attached. I tried to turn it by hand but it didn't move.…