Man.. what from what I've read, etc.. don't bother.
I've never seen a pusher fan which can move as much air as some of the pullers out there (Mark VIII, viper, etc), and at speed, it'll just be a big air blocker.
Want to hear something mind-boggling? I had a '95 Jeep Cherokee, with a mech fan, and an auxillary (factory) electric pusher fan.. mounted behind the rad (same side as mech fan.) .. pushing air through the rad. against the force of the incoming air from driving... who the heck developed that brilliant idea.