If I am reading this correctly, you are looking to add a sucker fan in the front of the rad, that would pull the air out of the engine comparment..... I don't think this would work and would be very surprised if the results were any better than not running a fan at all. the air being sucked thru the rad would be displaced by any air being forced into as you drive forward.
I would keep the flow going into the compartment and add some louvers to the top of the hood to aid the circulation.