Jaycee, the guns can be removed by applying an alpha channel to the part of the texture sheet that maps the guns. Here's a P-38 with painted on cameras (not nearly as nice as your modeled on ones) and alpha-ed-away guns. So if you like, you can make the nose the right size without having to show the guns. In fact, most parts of an airplane can be removed this way (on some you have to delete the .mos file for it to work), which is probably right up your alley.
Thanks gecko for that little snippet, that may come in handy in the future, you'r p38 looks excellent by the way.