I used a unibit to drill all 5/8" hole callouts for snap bushings in fwd and aft center sections. CAUTION- On the aft section, the two holes closest to the centerline have a lateral dimension referenced from a rivet in the spar caps. It would be easy miss this because it looks like you should measure from the adjacent vertical line of rivet holes in the spar web BUT if you do that, they will be off by about 1/16". I believe this would lead to an interference problem with a seat rib or stiffener a couple of steps down the road, so I'm mentioning it in case anybody reads this in the future. Most of the match drilling is pretty straightforward, but the aft section has a couple of 5/8" thick vertical bars that have to be match drilled through the spar web in two places for AN426AD4-14 rivets. Chances are high that you could drill these crooked if you tried to freehand it, so I used a 6" long bit in a drill cup with lots of Boelube and it went fine. You also have to countersink these bars on the fwd side so that the mfg. heads don't interfere with the wing spar stubs when you mate the wings to the center section. Once all the match drilling, countersinking & deburring was done, I swirled some zinc phosphate primer in all the holes with a q-tip. On the outbd lower 5/8" holes, they give you a pilot hole, so it's not like you can mis-locate them, but on all 4 corners, there is an interference where the F-704C or D overlaps the hole by about 1/16". It's close, but I'm not sure I could get a snap bushing to lock in there without whittling one side down, which sort of defeats the purpose. I emailed Vans to see if they had a problem with me relieving the interference by removing a little material from the F-704C&D. The word I got back from Sterling in builder support was that I could remove material to match the radius of the hole in the spar web, but they don't recommend that I take off enough to accommodate the flange of a snap bushing. No problem- Once I file the interference away, I can just push a bushing in from the other direction, per the note on the print.