Another take on the legal issues.
The pinups were artwork and as tulsaboy says, they vary in their degree of originality. There probably are some people out there (or their heirs) with some rights in them, but most of them don't even realize it and it isn't likely they would enforce them.
Tulsaboy is right about the Belle and also watch out for several bits of nose art which are in the Commemorative Air Force collection and as to which they have registered trademarks. Whether those marks are valid or not, you may desire not to antagonize them.
Also, original artwork applied to warbirds by latter-day restorers and operators is subject to copyright and they might be inclined to enforce their rights to protect their own souvenir sales, so I'd avoid anything that I see on a restored warbird unless it's a faithful copy of a WWII original. I.e. don't do "Ol' 927".
Finally, if the WWII original is a very close copy of, say, a Vargas pinup, then the original nose-art painter might not have much of a right in it, but Vargas's heirs (or Esquire magazine, or whoever) still may. Vargas and Esquire blessed the use of their artwork by wartime servicemen wishing to adorn their aircraft but they wouldn't necessarily bless the copying of it by a modern artist, even if filtered through airplane nose art.
Matt Martin wrote:
If it becomes a case of not being able to publish the work, I will post the art on the internet.
Posting the art in the net may constitute publication and will still be infringement as to any work that you couldn't publish. Many people don't seem to realize this.
Good luck and have fun!
August