I made up this tool in the photo, gave it away several years ago, and lost track of it, otherwise you cold have had it. The threaded parts I think were 7/8” fine. It took 2 days on each head and don`t think I would have got them off with the engine in the car. Once you have managed to get the head about 12mm clear of the block, very carefully hacksaw thro` the studs. They will probably need pressing out of the head, but what`s left in the block usually comes out easily. Good luck.