Good job, Tom Hawkes!
Now I found my better caseback opener and got the missing dimensions for the crown shaft.
Tube outside diameter is 4,5mm, inside is 2,15
We got 2,5mm of way from the outside surface of the crown to inside the case so th max. stem length is defined by that. Since the tube bore goes through in the same size all the way we could extend the crown shaft up to 0,25mm inside the case, the thread length of the stem allows that.
The gasket inside my crown is 3,3x1,8x0,5. My crown stem is 1,8mm thick.
Conclusions:
We should make the ditch 4,8mm wide. The rim around the ditch could be even 0,6mm thick as the outer diameter of that rim is 6mm at the gen crown.
The crown shaft that will take the thread for the movement stem is supposed to be 3,25mm long (from the backside of the crown as reference point)
The thickness of the stem shaft should by no means exceed 1,95mm. I