My LSD2 had a similar mount. I remember hanging up side down that knuckle had a natural tendency to loosen up.
Here is what I would do... Take the knuckles off, put them back in the box, and forget about them. Then use mounts which screw into the 3/8" thread inside the body of the mount. Use big pliers if necessary to get the knuckles off. I don't think you will break it.