Threaded Shackle Frame Mount

So here’s the story-I’ve got 56 cj5 with a rusted out frame- picked up a m38a1 frame to replace it. Both have the threaded shackles that mount into the threaded bushings in the front frame rail. So everything should swap over just fine, but the threads are stripped on one of the inserts in the m38a1 frame. I figured could cut one of the bushings out of the old frame, clean it up, and put it on the “new” frame, but after cutting the obvious welds on the boxing plate, it seems like it’s welded to the the frame rail from the inside-behind the boxing plate. That would making getting the old one out very difficult, and even more difficult to re-install correctly. Though I know it can be done,since these threaded inserts are available as replacements.

So my questions are:
Am I right about how these are attached to the frame?
What does it take to replace one?
Am I better off swapping to unthreaded shackles, and if so, what does that take?

 

Originally, the hangers are riveted to the frame, and welded each side with two welds. You should be able to see the heads of the rivets.

 

It doesn’t thread in at all, just slips through.
My concern isn’t so much getting the bad one out, but getting the new one installed properly, since I’m not quite sure what’s going on inside the frame.

 

I ended up replacing the "C" threaded shackle with a Warrior solid style shackle with the same center to center distance as the threaded C style.
Threaded holes in frame were beat up and I was replacing front springs at the time so I saw no need to try and replace them.