The top grill I just blocked with coroplast, I don’t think it’s much of an actual intake on it’s own anyways.
For the lower grille, I found this thread:
https://ecomodder.com/forum/showthread.php/civic-lower-grill-block22280.html
I thought it would be a lot harder to make a block outside the recess, but it looks like it’s more straightforward than I thought. I’m just going to copy his work, and add a sliding panel where he put his cutout. That bell mouth is sleek, and a very smart idea, but I think I’m a bit too lazy, atm. If I can find an easy way, I’ll make a bit of a crude bellmouth on the intake cutout in the lower grille block.