Right spar, lower flange only: After getting all of the holes countersunk, I did some scotchbriting of the holes on the flange to knock down some very small ridges around the circumferences of the holes. It only took a few light passes to smooth things down; not even enough to disturb the anodizing. I followed that up with a solvent wipe and rattle can primer. After dinner, I went back out and riveted in the 30 #8 fuel tank skin nutplates and 12 #6 access cover nutplates.
One note on the locator jig. I worked on this thing probably half the day before coming up with someithing I thought would work. When riveting the nutplates on, I ran across one screw hole that I had inadevertently missed countersinking. With other nutplates in the vicinity, I couldn't get the jig where it needed to go so I just riveted in the nutplate and used Van's recommendation of using it to locate the countersink pilot. It worked great, and no damage to the threads as I had feared. The jig worked well enough, but using the nutplate was so easy that I don't think I'll ever use the jig again.