Been a while since I have posted but I have been keeping an eye out. I apologize ahead of time for the poor quality of photos. I've had this watch for a few years now on a trade. But have been unable to find out much about it but I have not looked very hard either. No one that I have taken it to has the tool to open the back. It's a bit unique for the Omega watch.
Late 40ies / early 50ies bumper. Possibly model G 6518: https://www.omegawatches.com/de/watch-omega-us-collection-omega-g-6518
Probably an earlier bumper as noted because the case is a little different but mine is a later caliber 500 gx6267 nearly identical dial.
You might have some luck opening the case using a wad of painters tape with sticky side out, press gently on the caseback and turn counter clockwise to open it, may open easily.
US market Wadsworth case, ref G6525. Note the case back is in two parts, outer notched ring and inner cover. Gold ring on OPs watch indicates a solid gold case, similar GF cases had a steel ring.
Thank you for the replies and all of the info. I should have included it was a bumper. I was also told by trusted PO it was solid. I traded my old Speedmaster Triple (that I found out was real, but black market). That was a few yrs back, but sounds like it was a good trade. So, with it having a two pcs screw back, I don't think the tape thing will work. Any advice about opening her up?
The outer notched ring is threaded and screws into the case holding the back in place. See the photo I posted above. If you don't have one of these you can use a good quality (I would not recommend one of the cheap one off the internet) adjustable case wrench as in the last photo.