Most times unit markings face front on both sides when they're carried on both sides. I don't see any good photo reference online but this should do if it's accurate-
I'm pretty damn sure the Eagle decals of Hahn's planes are accurate, or so say all of the photos and first hand interviews in the Assi Hahn book by Crandell-
I'd be 99.9% sure they would face front on both sides. If you want to be really sure find some photos specifically of the plane you're doing. If you're basing these on conjecture, who's to say?
On to your other problem, first, we need to know what application you're using. In Photoshop, simply flip horizontal. You can copy/paste/flip horizontal and slide it into place. If you've already got the duplicate in place, select it and flip it. You'll find the flip command under Edit>Transform>Flip Horizontal. Any other application and you'll need to wait for someone else to answer.
