Thanks for the massive amounts of replies, guys. I'm really not looking to zip-tie it unless I have to. I do plenty of body work on classic cars and I'm not trying to take said shortcuts. All aftermarket OEM grille pieces are NOT complete sets/parts. There are three pieces that have to be bought individually, and the CASING (the part that attaches to the bumper) is not sold to my knowledge.
If anyone can find that piece, that'd be great. Under the car, there seems to be no bumper damage to where the casing attaches. I'm going to look into that part from the UK, for now. I suppose I could go to a junk yard, but I'd rather have my own in red, or black.
I'll post pictures of my Mustang and Comet Caliente eventually.
Please keep the responses coming, I really appreciate it!