OK all, I had the same question. I have gotten my new Stillen cover and wanted the SS speed grill to match the upper grilles.
What I did was ask Josh @ Stillen to send me the largest SS grille they had...and I would modify it to fit the Stillen opening. What they sent me was a Ford Excursion main grill. This worked out perfectly!
#1, try to do this before you are painted, otherwise lay down some masking tape to protect the paint as the SS grille is sharp!
All you do is make a template, with the cover on your bumper (preferably off your D). First, cut a piece of cardboard bigger than your opening. Get either a screw or what I used, an allen wrench and poke through the cardboard to hold it in place while you trace the opening with a Sharpie.
The Ford grille is already formed to the Excursion, soooo, you'll be able to use one pre-formed edge. The others you'll have to trace around your template, draw another line about an inch away from your template line, and then cut out with snips. I used a set of lineman pliers (electricians pliers) because they have a broad face to bend the edges over for mounting the grille. Test fit and make any necessary adjustments, mount using the SS clips and your done.
Seems like it would take a while, but after I took the bumper off and got going, less than an hour later I had an SS speed grille, custom made!
Here's my offer...I would be willing to make one more for someone else, if you'll pay at least half of what I spent + shipping. That's about $80.00. Let me know.