Step 17. In trying to fit the doublers in what I thought was the right way, I noticed that the inboard halves stick above the spar webs about 1/8 inch. As it turns out I had them backwards. Switching them put the inboard haves pretty much flush with the spar web top and bottom. Another issue was that when I originally built the horizontal stabilizer I hadn’t completely removed the flange radiuses on the aft side of the spar, so I had to trim those and debur the fresh cut edges. Note the trim lines in photo 1.
After a couple of trial fits horizontally, trying to line up the bends in the two parts, I finally just measured the distance between the bottom rib holes and the next holes outboard on the HS-702 spar webs and marked the midpoints. This point lined up perfectly with the bottom prepunched hole in each of the doublers, and left plenty of hole-to-hole and hole-to-edge distance for all of the existing holes in the spars once transferred to the doublers. The interference with the vertical stabilizer attach plate warned about in this step is non-existent, with about 3/8 inch clearance on both sides. (Photo 2)
After getting the doublers clamped in place and edge distances checked and double-checked, I matched drilled and clecoed the 6 center holes and the 1 each top and bottom holes in each doubler as called for in Figure 7. (Photo 3)