I never did get the measurement but I'm now within 1/4 inch of square using the tram guage. Aside from the frame being diamond, my biggest issue turned out to be the rear spring mounts. They were so twisted that the springs wouldn't line up in back. I replaced them, pushed the the diamond out, and everything lined up as it should. My Jeep now handles way better that it did. It's actually fun to drive now.
I couldn't get a frame shop to touch it. No one wanted to work on a 30 year old frame. Too much liability they all said.