I decided that now was the right time to pin down the close-out ribs that go above the torque tubes. Next step is to install the pushrod linkages, which would block access to the rivets that need to go into the ribs, making it much more difficult.
As I’ve written about before, these torque tubes are ridiculously difficult to get aligned just right so that they move smoothly. The fit of the closing ribs also plays a part in this, since the plastic bushings on the torque tubes are pinched in place by the closing ribs. So, after a few more iterations of adjustments to the ribs (little bit of sanding here, little bit of shaving there), I used a C-clamp to hold the ribs in place (rather than clecos), and then installed rivets, reaming holes as necessary. I think I was successful, as the joysticks still move pretty freely after I finished riveted the ribs.