Thanks again to everyone for the support!
@Iceballer regarding the drill press, you can use a dremel/hand drill just be careful not to brake the bit in the case. Go slowly and try to stay as perpendicular as possible; you my want to use a slightly smaller drill bit in order to account for the non perfect alignment.
Unfortunately there is not a specific amount of material that needs to be removed, I just looked at some references from the book "Submariner history" by Mondani and tried to keep everything balanced. Fortunately as
@Karbon74 mentioned there is a lot of margin for errors since the watch is pretty old and no 2 cases are exactly the same.