Had to take a hiatus: first for business travel, and then for more important things such as time with children.
Vans instructions note that you should leave out a few rivets in the HS inboard ribs, in order to install nutplates later to hold on a fiberglass fairing between the empennage and the fuselage. Wait a second... shouldn't these nutplates be installed now?
Sure enough, others have figured this out too -- not always prior to closing up the HS, unfortunately. Bought some nutplates on eBay, ordered rivets to hold them in, took a deep breath and drilled/dimpled/riveted/squeezed.
Of course one of the two parts involved was already installed, because I didn't come to this realization until well into things. However as of tonight the first rib is ready to install. Hopefully the other side will go OK, since one end is already riveted in place.
Time: 2 hours