I'm hitting the same point in the build, and the drawings just don't make clear what part goes inside or outside of what other part.
I have slid the tip skin inside the elevator skin (which this thread says is the right thing
), but I'm still left wondering if the E-904 flange should go inside or outside of the front spar (or, does it matter?).
I think this picture illustrates the question:
From bottom to top, it shows the E-1001B elevator skin, E-913 tip skin, E-1002 spar flange, E-904 inboard tip rib - is that the right order, or should the E-904 be below the E-1002 flange along with the tip skin?