Just remember with grill blocks that you do need some air to get to the radiator, just not as much as factory. Also check to see where the air intake is so you don't block that off completely.
Here's a sample using your own car pics:
ok, the second isn't one of yours.
In the top pic, the stuff in red can definitely go. I'd probably block the chin hole too. The yellow I'd block and slowly open from the bottom depending on engine temp stability.
In the second, block those side scoops and you can probably do rear skirts pretty easy.
Putting your car's shape thought the flow illustrator, the rear wing may or may not help your aero.
Here's a gif. That'll take testing to know for sure.
I like mustangs, my cousin had a similar one. I can't ride in them though because I have to tilt my head to the side to not hit the ceiling and even then all I can see is sun visor
