If it is a replica of an actual fighter from the war that did have the kill markings on it - ie. same colour scheme/serial number etc, then yeah sure, as you are effectively re-creating a memory from history.
If it's not going to be an actual accurate looking replica of an actual plane, personally I wouldn't say it would be inappropriate as such, but to me wouldn't seem "right" and would be annoyed only as it would not be accurate.
The reason I think that, by putting it another way... eg. the swastika was obviously the symbol of Nazism during the war, and was stamped on virtually every German aircraft/tank/warship during the war and nowadays symbolizes the evil regime that it was, the symbol that signified the murder of millions of
non-combatants. Now, if you were to build a replica BF-109, would you paint a swastika on it - of course you would! Would you think it "inappropriate" by seeing a BF-109 with the swastika on it at an airshow - of course not!
My point is, symbols such as the "rising sun" signifying the successful kill of a Japanese aircraft on the side of an allied aircraft, or the swastika on the side of a german aircraft, are totally acceptable. Just do it correctly, and accurately - not just for the sake of doing it.
If however you were to put either of these symbols on your tshirt, THAT would definately be seen as distastful.
Bloody hell I have just written a novel - sorry!