Here is what I learned from the process. The first grill took 50 minutes...the second was ten minutes.
First, use the original grill or pattern of the exact diameter to draw the pattern on the new material. A contrasting color/sharpie helps.
Second, use tin snips to cut away the large areas of material. Just straight cuts...don't try to follow the circular patter very closely. And Always err on the side of leaving extra material rather than trying to cut too close. It's easy to cut away more material later, but pretty tough to put it back on.
Next I used a grinder to carefully shape the outside of the new grill going slowly and getting a true circle. On the second grill I made a plastic template, same diameter as the stock grill, and held that piece sandwiched with the new grill and used it to put the finishing touches on the new grill with the grinder. Don't forget to take the burr edge off the new grill as it can be very sharp.
Last, I tried a couple different kind of paints. Krylon semi-gloss worked best. It dries quickly and smooth and the color seem to coordinate with the paint on the cups very well.