That's a great explanation, Steve. Makes a lot of sense and is exactly the kind of fix that could be done quickly, a field expedient fix.
@Jeff N.
Jeff, does this explanation change how your measurements effect the fit of 2-2-V-1 into the window opening?
No.
I don't find it to be an 'explanation', but honest conjecture about a 'might be', which - no offense intended and with great respect for another's idea, is not a likely possibility to me as a sheet metal mechanic with engineering experience as well.
Were I to add ad hoc vertical bracing such as I had earlier conjectured as an explanation for the horizonal stiffening of the panel, I see even less reasoning to not pick up the remaining ring structure at STA 307 than I would to abandon the existing longitudenal bracing in this area.
Why? Two primary reasons:
More criticality as to shaping - the curvature is greater in the vertical than horizonal (we're looking at the side of a slightly bellied 'barrel', whose 'ends' are at the fore and aft (right and left) of the fuselage section involved; continuity to the existing ring former would in that sense be more critical, in my view.
Relative ease of attachment to existing structure: it is simply easier to base the top and bottom ends of a vertical replacment here at the existing STA 307 structure than to let it 'fly' with nothing else to tack it to but skin (above and below the window opening);
in the case of fore and aft stiffeners, we are simply coming near ring structures beyond the fore and aft ends of the opening and may attach at virtually any location that is convenient, within reason.
These are merely my views - YMMV, of course. But no, it doesn't change my view of the fit issue.
One danger we face in 'brainstorming' ideas to explain how 2-2-V-1 'might' fit is that we can get way down a path of conjecture that lacks real clues. What have we seen - other than 2-2-V-1 itself, that supports the idea of off-setting members such as the conjectured vertical bracing (away from STA 307) and conjectured horizontal bracing (along the parallel rivet lines on 2-2-V-1)? This is one area I suggest we have at times strayed too far in, IMO; I found a personal need to stay more critically grounded in my conjecture and technical review as the study wore on. To each his own, of course - but that is what I came to, as inconvenient to me as it proved to be. I don't find it to be a loss, however, but a more robust way to research such things, IMO.