if i do a grill block i plan to buy a new radiator.
my car has the top and bottom grill opening. The top one can be covered over permanently and the radiator can be moved to the bottom one.
The new radiator will be the same width but only as high so as to cover the opening and then made deeper to compensate for the missing bit at the top.
Believe it or not it should make the radiator more efficient as before there were always parts of the radiator shielded form the airflow. Some ebay door sealant around the sides of the radiator to the bumper and hey presto
The extra airflow will be allowed through as it can, always cooling, any that can't will be forced over the car or around the sides.