J-heads

Thanks to whom can help. Dont want to sound stupid but what is a j-head? I have a used engine with these on it. They are on a 360. The heads are stamped with a "J" . Should I keep this engine?

The letter is a casting letter. There good heads and resond very well to porting. I would keep the engine and heads. Build to suite. It's an excellent platform to spring from.