[Vlad95]

I still disagree with your sawing or cutting method. It is much easier in terms of the opening method and better in terms of preserving authenticity to simply flare the joint of the body and the lid, and then restore the flare again. If you do it more carefully than I did in the photo (I was just lazy, and this particular device was not particularly valuable), the result may be indistinguishable from the original.
You don't even need a special tool for this. I got by with just a thin screwdriver, pliers and a small hammer.