Tonight, I started riveting the wing ribs to the left main spar. It took a few tries to get the first few rivets set satisfactorily, but once I got the technique figured out and got back in my rhythm it proceeded much more smoothly. There are 14 ribs (but the 1 outermost doesn't require riveting yet), and I did all but the innermost 3 ribs in this session.
While reading some VAF forum threads, I found one that revealed that I should have cut the short J-channel pieces a few days ago from the 8-foot stock rather than the 6-foot stock (which have a specific purpose later on in the fuel tanks). This means that I'll probably be ordering a new 6-foot section of J-channel prior to being able to finish the right-side fully.
What's next? I need to finish riveting those innermost 3 ribs, then retorque all of these bolts