i was looking for johnny joints or flex joints to run
Can you measure the width of the opening for the axle side mount from JBA?
This will tell you what widths will work.
You have two options but only one I would personally run. Because the JBA kit uses female rod end joints you would need to fabricate a female-female coupler which may cause issues on the length of the arm, and you'd need to weld one end so it doesn't loosen up.
The way I would do it is purchase new DOM tubing and weld in
thread adapters
Once I finish my 4 link I'm going to look into making a kit that will bolt into the stock location and is fully adjustable. Just need to speak with my lawyer about protecting myself and liability/insurance. My buddy who is an automotive engineer and I have been talking about making poly bushings and other parts for the KJ.