Here's the tricks my machine shop friend taught me. He works on many vintage 30s & 40s engines. First you heat the stud not the head. Then quench the stud with a spray bottle. Try to remove it gently. If it's still stuck repeat. Still stuck? Reheat and melt a candle into the threads, cool and try again. I would also recommend the Craftsman stripped nut remover set. It's about $25 and grabs about anything. I've had this method work nearly every time,and I've done quite a few.
Good Luck
Doug