I made some progress today. As you can see everything I need is at hand:





As said before, I marked the shape of the headstock and took my handsaw to cut it out. I'm pretty happy with the result



Next, I taped of the neck and started sanding. I started with grid 120 down to 150, 180, 240 and ended with grid 320.



I did the same on the back and side of the body and everything is feeling very smooth now.