Ok So quite a few people have asked me about where they can mill and how much, so what I have done is created some images which give you a better idea of where the material is and is not. I've taken the outside surfaces and made them translucent (I wish I could do that to people's clothes... but I digress).
It takes a little looking at to understand but I hope it helps. You can see the ghost of translucent outer surfaces and then the solid colour of the inner surfaces. You can see the main valves tube, the area for the breech thread and the sear location and cut out. You can also see some dimensions as to how thick the material is... note it's not very thick in many places! Dimensions are in mm.