Like everything it takes longer than you think; probably 8-10 hours to work through 14 brackets for both wings. My process basically is to use the offset #12 hole and a scrap nut/bolt to mount the bracket to the Spar per the plans (some brackets face different directions). Ensure the bracket is 90 Degrees, then use the pre-drilled spar as a guide to drill the other two holes in the bracket. I use my 90 degree drill attachment because it is much easier to ensure that I am drilling exactly perpendicular to the spar. This makes the holes as perfectly round as possible. The AN3 Bolt fits into a #12 drilled hole perfect if it is drilled well. Almost creating a friction fit even without the nut. Anyway, after the 2nd hole is drilled I drop in a bolt just to make sure the 3rd hole is drilled perfect relative to the first two. Here are some pics:
After the holes are drilled, trying to get the nut plates on is also a challenge. To keep the nutplate as centered as possible I use a scrap bolt and nutplate as a jig and use my drill press to ensure the hole is straight. A non perpendicular hole will allow the nutplate to shift when riveting and possibly offset the nutplate to the drilled bolt hole. Perfectly drilled holes are Awesome and Important ! (Am I a dork or what) ;-)
Once the nutplate holes are drilled and countersunk, its off to prep and prime before mounting the nutplates, then mounting to the spar. (These will only be temporarily mounted to the spar and will need to come off for tank final assembly.)
Side note: I have also finished match drilling both wings top and bottom as well as leading edges ! Wahoo.. Now its time to focus completely on the Tanks.. These guys will be a challenge and take some time but I look forward to it.