After I had drilled out or sawed-off everything I could think off it did still seem quite impossible to get of the rear body. I had to ask the the panel beater for advice.
He did look at the problem from several angles.
After an hour or so, he came to the same conclusion as I did. It´s the sharp angle. It´s to sharp and there is to much material. There must have been a very skilled person who had filled in an extra strip with aluminum. Without leaving any sign.
A few days later I dared to try to bend out the upper side panel of the body. I soon found out that we were right. The sharp corners at the rear side windows had to be finished with the body in place.