I taped it up real good with the blue masking tape so the chrome finish wouldn't get scratched and it gave me something to draw a line on. Measure really good and then measure again before you cut! If I remember correctly (it's been a while) I cut about 1 1/4" off the bottom. I used a jig saw with a fine blade and went real slow so the plastic wouldn't melt back together. After cutting I used some 220 paper on a block to smooth the edge and put a slight champher on the chrome finish so it wouldn't chip or peel later. The top mounts with the same four screws as your original grille. On the bottom I used a screw about an 1 1/4"-1 1/2" long in each corner of the honeycomb part of the grille and screwed it into the header panel behind. I painted the heads of the screws black and you can't even see them.
BTW, the bumper can move up or down by loosening the four bolts that hold on the tow hooks in front for a perfect fit.
Again, I can't stress it enough, measure, measure, measure!!!
Good luck, it's really not that tough. I'm going to put in my updated headlights as soon as I get a new conversion harness.