Mine was for a commercial bumper. Pick up the phone and speak to Alex he won't bite. You have to take out the 2 corner trims first then pull the mouth piece with the foot holes. Do a bit of cutting then fit the new mouth. It's a case of cut a little try it in then cut a bit more till it fits.
When mine was painted it was filled in a few little places and fitting was easy. When you take out the old grill you'll have to cut out a bit of plastic off the bumper, best to get it to fit first before you get any thing painted, you can make out where I've cut the 2 bars that go down
And here it is fitted in, didn't need to glue it in as it was a good fit