That is casting flash left over from the sand casting process. The foundry will usually break that off with a hammer and what you are seeing is the remains. That can be removed with a die grinder and carbide rotary file before the head is assembled. It is kind of like porting, but for the oil returns. You will also find those all around the outside of the block and heads, wherever there is a parting line in the mold.
Some theories for removal of the casting flash include: Less restriction for oil returning to the pan. Reduced stress risers. Remove sharp edges to prevent injury during handling. Or you can just be cool so you can get all the chicks and polish the outside of your block and heads, blending in all the casting flash so your engine has a show-quality paint finish.
No worries brotherman. If it was going to break off, it would have done so by now in a now 40+ year old casting. Not to say that there aren’t casting flaws in bocks and heads, but I think your gaskets would go long before a chunk of your head will fall off.
Cheers,
Joe
