I agree with Bruno; if you're already committed to the AT screen, just get 3 in-cabinet M80's. Not sure what to tell you about your upside-down v. right-side-up issue. I guess I'd need more information about the room to have an opinion. How far back will you be sitting? How high is the ceiling?
I think you'd want the tweeters - generally - at about ear level, but that having them "a little" above ear level would probably be fine if you're far enough away.
Sounds like a very exciting build; I will look forward to following your progress.
