Sigh...I had to rebuild the spar box/tunnel, as my first version did not have enough material supporting the rivets on the upper angle drilled through the top of the box. In order to keep the same problem from happening again, I needed to re-make the front of the spar box. I didn't like how enlarged some of my dimpled holes had become on the rear box, so I just threw up my hands and did it all over. The only parts I kept were the side shear gussets.
This operation was pretty slow-going, as I had to match everything to existing drilled parts and make sure it would all fit back together. One thing that made it go faster was for the sheet metal box parts, I used the old parts as templates (since I know they fit well in the fuselage). I just otlined the onld parts agains the new sheets, verified the measurements against the plans, and started cutting. This worked great!
The really good news is that it all came out great. I realized that part of my problem with the first build was that I didn't clamp the spar box front-to-back, letting the parts naturally find their shape. Using some bar clamps, I found I could precisely control the depth of how the top angle sits in relation to the pilot holes on top of the spar box. I used the stiff edge of a yardstick to make sure the inside of the spar box stayed straight and was not bowed.
