Having previously primed the under side surfaces of the side rails and gusset thingies, I riveted them together. If you want to use solid rivets for these two holes, you pretty much have to rivet them together now...before they're attached to the longerons. The sharpie line was actually helpful in aligning these since the holes are really close together, but they are long parts.

I spent some time hacking up some plywood (leftover from the shipping crates) into platforms that I could use to lay upon when bucking the top skins in the tail cone. I had talked with my friend Tom Webster about how to do this. He recommended using thin plywood (so it would flex) and resting it upon the lower center rib. Since the center rib sits up higher than most of the bottom edge of F-706, I wanted to be sure I didn't bend that edge over, so I cut out another piece of plywood for the baggage area and propped the forward edge of the tailcone plywood on a piece of 2x4.

Here are the little .032 thick shims I made to go between the sides of the F-706 bulkhead and the forward top skin.

You can see how they fill the gap rather nicely.

Update: After riveting these in, I think it would've been slightly better to use two layers of .025. One shim would have been long enough for the two holes shown here and the second layer would've only been for the bottom hole.