If the hood vent is sufficiently large, a duct could be made to seal the vent to the radiator and redirect ALL cooling airflow out the hood, avoiding airflow over the non-aerodynamic engine block entirely. At that point, a grille block may be superfluous.
Keep the grille block, make sure that it is aerodynamically smooth and preferably directs air flow up over the front of the bonnet/hood. Then hoping there is room for the next bit, tilt the radiator forward on its mount, modifying any duct to the hood/bonnet vent that you have already put in, then, build another duct to take air from behind the front bumper/airdam to the radiator.
Now you will have a flow through system that takes cool air from under the front of the car, reducing uplift, through the radiator and out the top into the existing low pressure zone. Unless you do a lot of slow up hill heavy stuff, the low pressure zone will hopefully be enough to avoid having to fit a second fan.