I found this on my head too, but only on one jacket. I didn't have a head gasket to check against so i figured that l would just weld it to make it suit the others, like you said it seemed close to being able to creep under the head gasket. So l'm guessing in my case its a casting problem. Nice build though, clean looking car. Are you going to flow the heads? or was the port polish job just to clean them up?