Use hard AC foam from Lowes to fill holes
I used metal pieces screwed around the radiator sides to block the air from
bypassing the radiator.
Then used 2" foam from Lowe's to fill the gap at the top of the condenser
and around the sides not filled by the metal pieces.
Works great and car run cool in heavy So Cal stop and go traffic with the
See the before and after pictures - lightish gray foam is installed in these pictures.