As someone who owns the original version of Airship Pirates, what I'd ask is why you'd want the setting rather than a new set of rules for it. It's one of the few RPGs that I've bought because it looked cool and then later regretted. The background is bad and the rules aren't really anything to write home about.
Honestly, I'd advise you to just grab whatever ruleset works best for you and then adapt it to a setting that has Airship Pirates. I guarantee that any gamer into the Steampunk genre could create a better setting than Abney Park did just brainstorming on the premise.
As you might guess, I'd suggest looking at the OneDice system simply because I feel it can't be worse than the original Airship Pirates ruleset. But not before looking at other rule systems for Steampunk in general.