That is freakin' fantastic Ken!
I modeled a ball joint that you can 3d print and is sized to attach to PVC jsut for a project like this if you would like the STL. After looking more closely at your joint I am digging the wingnut and teeth configuration. I am betting yours will work better for your application.
I think a lot of us with PVC mannequins would love to print out something like this for our builds!
Glad to see the progress Ken!