Working, now properly usable on portrait. Oddly, it's not quite centered when it is full-width; but it's close (I don't care if it's dead center...) and it now fully displays the left pad when the navigator is on the side.

Great!

And of course, the two buttons (Shift, Alt) work well now; I had intended to suggest that one or both be used as indicators.

Along those lines: What about the pad-swapping? If Alt and Shift were consolidated, or perhaps alt moved to the &!e' key, you could also have an indicator/control for that. Maybe even have it latchable... a double-click on the swap button "permanently" switches the pads, instead of next char only?

Just thoughts here; I don't really see a major usability shortcoming here, the way it is.
Well, maybe using Gnumeric; you wind up wanting the numbers there. But, there's always full-screen and/or moving the panel to the top where it belongs.