Removing Stuck Heads

[Ken/Alabama]

About a year ago a friend called me and said he had a couple flatheads in his shop that had been there for years and were in his way and he would bring them to me if I wanted them so I said absolutely. He brought two 37 21 stud engines and a third was a 59L with offy heads . I could tell that someone in the past had tried to remove them because all the nuts were gone and I could see some marks from failed attempts. So I sat it in the floor and would soak the studs with Kroil oil . I put it on the engine stand yesterday and pulled the oil pan. To my surprise it’s very clean and has a Merc crank in it that still .010/.010. I pulled the crank out and five pistons out from the bottom. It has a set of Jahns four ring 3 3/8” pistons. I put a large block of wood down in the cylinders from the bottom to try to drive the heads off. They never budged. Next I’m thinking about welding nuts on the studs to see it the heat will break them lose. Anyone have any other suggestions. ? Thanks