Freddy
I knew there was something I had to do to this case.
I got it from toomuchgear who said he got from Silix, it came with a rivited oyster but when I removed it to put on a nato, the number to my surprise was 6452, I was thinking it may have been for an old turnograph, but GMT makes more sense, ( sorry I dont have a picture yet) it may be worth checking with Silix to see if he cant get hold of these still. $150-190 eta movement.
I've been thinking I need to experiment with a cheap of 21j gmt movement
I'm looking to get insert from the bay, Im sorry I dont have the size of the bezel for you
Not sure if this will help but good luck with your project
ST4