FYI, you should change the gear oil in a ZF annually. Next time you do that, stick your pinky through the drain plug hole and see if you can feel the ring gear bolts. If you can, you should be able to tell if they are safety wired or not. I’ve never tried to do it but I am told you can. Failing that, buy or borrow a borescope.
Perhaps Bosswrench will chime in. He would know if the pinky trick works.