Im sure the push/pull config will reduce distortion - John Sheerin did something similar in a dual 10" CSX basshorn, and noted very good improvements in 2nd HD.

Ducting to get cool air from the outside - reminds me of the cold air intake/induction system I put on my car made from 90mm piping :P If you were to do the ducting on the vented pole piece, I think make the piping larger than the vent itself so that the airflow doesnt cause a restriction and start creating noise and air pressure buildup of its own, which would mean more distortion.

Adrian