Everything came together today to work on this project.
I talked to the customer a few weeks ago and convinced her that padding out the width of the jamb was a bad idea. So, we decided to shim only behind the edge of the bi-fold door panel.
When I got my framing square on the door, I found that the top jamb was not level and the hinge side was not plumb (contrary to my earlier statement). The latch side was plumb.
So, I fitted a ¾" x1 ⅜" spacer on the hinge side jamb, just outside of the old built in 'stop'. Then, holding the door panel assembly against the latch side, I scribed the top and hinge sides, took the assembly down and used my power plane to shave down the panels to the scribed line. Mounted the hinges to the panel and hung the assembly in the opening. It looks fine as the 'adjustment' on the panels is hard to detect.
Need to tweak the stops a bit and mount the latch, but, the hard work is done.
Thanks for all the great ideas, Bob.