I redesign this blower duct http://www.thingiverse.com/thing:560790 in order to fit into my flashforge creator pro.
I used this blower duct with a SUNON GB1205PHV1-8AY.GN (http://fr.farnell.com/sunon/gb1205phv1-8ay-gn/turbine-50x50x15mm-12vdc/dp/1568490).
Don't forget to print the blower wedge otherwise your blower will touch the frame of your printer at the home position.

I also made some modifications into my MakerWare configuration files :
##ReplicatorDual.json

• change the Y platform_length to something smaller (140 for me)
• replicator_start_position set it to Y61 instead of Y75

##start.gcode

• change Y72 to Y61 for the line beginning by G92