All the advice from everyone is good except they seem to forget one thing.....Its a 1973 360. im not even gonna remind you of how old that is. your best bet is to drill out the hole and heli coil it to stock size. that is 5/16. If you cant drill it strait pay someone who can or pull the head and have an engine shop do it. Ive removed hundreds of broken ext. studs and bolts out of all kinds of heads and never had good luck doing That stud they are very difficult to say the least. metal stud iron head. you would think it would come right out but that is not the case with small block mopar outter ext studs. good luck