We did some D20 based Crimson Skies Role Playing, here for a while, but it was very difficult to reconcile Crimson Skies based air combat resolution with the various role playing elements. The game mechanics really just don't compliment each other, it proved conclusively that for me, a board game is a board game and an RPG is an RPG.
I think that maybe the most of the Crimson Skies air combat rules would have to be trashed so that combat resolution were brought more inline with the D20 (Or whatever game system you use) core RPG rules game mechanics, then it might become more seamless and story oriented as any good RPG should be. Map, movement and maybe aircraft stats could probably be ported, but the characters stats and skills would have to come from the host RPG.
I have played Deadlands D20 and like it. I have a few of the original Deadlands game books but I have not used them to actually play so I cannot comment on the game mechanics. Deadlands Noir does look interesting though!
Flying the Crimson Skies