That's awesome..
How about (think of "kills") putting on a small Japanese "Rising Sun" Flag with 5 or 6 hashes?
I think a few bullet holes would be the ticket, not many, just enought take up some space. Or, possibly list some B-17 "hot spots" kind of like the World Massacare Tour for the AK-47 shirts. Could even do a stylized flight plan map showing of major points of interest. Whatever you chose I'm sure will be top notch.
Looks awesome right now man!!! I really like the kill signs idea. Also what if you were to just move the star forward toward the 870 marking? It might break up the empty space and still not be adding anything that you don't want on there. I am nobody to make suggestions to you though. You are the man when it comes to stuff like this. Great job!!!
Looks awesome, as all of your work usually does!!
As for "Ruptured Duck", go here:
The Ruptured Duck - German WWII Memorabilia / Militaria
and here for an explanation: What Is "The Ruptured Duck?