Help with rear suspension...

[Portmod7]

That is a bump stop mount for the rear end. It is factory. You're missing the rubber bump stop that fits in it.

I've got no clue what that rear end is. You might check out the No-Limit panhard kit, it would probably fix you right up, I'm not sure how much it costs though. I believe it mounts the panhard to the right side trailing arm instead of the rear end housing, so it would eliminate using the mount that on your rear end. But, like tubbedII said earlier, if the previous owner didn't get the perches in the right spot, just the panhard kit won't fix it.

I believe there are other companies that make the same style of kit if you look around.