For future questions, I would suggest this excel calculator created by Paul Copioli:
http://www.chiefdelphi.com/media/papers/3166
It has an air usage calculator but also a calculator for center-to-center hole spacing for chain, and a in depth calculator combining multiple different motors within one gearbox.
Paul's Calculator and JVN's Design Calc are two things always open for me during build season for solving design problems like yours.