The guy that I bought from runs a shop called Scan Automotive. But he told me that he had another shop fabricate the bar for him, and that shop was called Specialty Engineering or something like that.
Basically, the end plates conform to the countours of the inner b-pillars (with the plastic covers off). From there, the two factory clip holes are exposed, as well as the b-pillar's sheet metal. This is where we finally put in our rivet-nuts, which allow threaded inserts to be put in securely without ever needing access to the back side of the sheet metal.
Here's a nice video to give you an idea of how rivet-nuts (a.k.a. threaded inserts) work:
What I did was enlarge the factory holes, so that I could put in a thicker threaded insert, the thickest I could find.
The trick is to find a rivet-nut gun or tool that can pull the threaded insert back through and tighten it securely so that it does not rotate inside the hole created. And the rest is as easy as matching a bolt's thread pitch to the pitch of the insert you put in
