Trimmed spar doublers per print. Drilled/reamed all the holes that take AN3 bolts. There are a couple of things in this step that would be easy to mess up. First, the 1/2" wide spacers get drilled for an AN3 and they have to be pretty precisely located to both support the spar&doublers and to not blow the edge distance when you drill that big hole through them. In order to do this, I took the doublers off and drilled the holes in just the rear spar to #13, then reinstalled the doublers. Drew a center line on the spacers, slipped them into place. Once I could see the centerline through the spar I clamped the ends of the spar/doubler fork to lock everything down, checked to make sure the spacer was square to everything, then drilled through the whole assembly. Reamed everything full size as a stack. The outbd edge of the spacer spacer ended up being 1 5/8" from the ends of the fork that is created by the spar & doubler. Also, the outermost -4 rivet on each end of the assembly only go through the F-705A & B, NOT through the doublers. If you don't get drill happy it's pretty obvious that you can't put a rivet in there because it's far enough outbd that the doublers have started to diverge away from the spar at that location. But, there's nothing about it in the instructions, or a specific note on the print or anything. The only way you would know this just from looking at the print is if you notice that the rivet callout for that location doesn't mention the F-605 doublers in the stackup. Got the entire spar final drilled, including all the seatbelt mounts. Next is trimming the extra flange material off the seat belt mounts, deburring and priming.