The stainless steel mesh I used was #4 from Racer Parts Wholesale 24x36" for 29.95. All you need is wide enough for the grille which is about 29". It is a little difficult to cut with wire cutters. Make up a template with cardboard. Take a piece of wire or two and attach the cardboard to the mesh screen so it doesnot move during the cutting. When done trial fit and then trim as needed. My opening had recesses around the opening so I added fiberglass filler(bondo etc.) and smoothed out. I then used stainless screws to attach it to the body.
For those of you that are interested, I did cutouts for all the vents as well to keep leaves and other road debris out of the various openings, especially the air vents to the rear hatch. Here are some pics or those.
These were made the same way as the grille. There are 2 ways of doing them. The first is like the originals. They are attached with metal tabs that are attached to the body. I will have pics of one next weekend when I visit one of the road cars. The second which is the way I, Bill Bayard and some others have done. That is To use vacumn tubing to hold the mesh in place. Do a cardboard cutout. Make it about 1/8 to 3/16" smaller than the opening. Get some 3/8" vacumn hose from your local parts store. Cut it to lenght, slice it along its axis on one side. Insert the stailnless mesh and press fit into the opening. Use some silicone sealer to hold in place. If you have a dark color, you can use the black silicone. With a little fiddling it will work. A sheet of 24x36" will give you enough to do all the openings including the rear radiator vents(oil and trans) and have a little left over.
There are a few tricks to doing this right.
1. Cut the stainless a little smaller than the opening(except the front radiator).
2. Slice the tubing at 90 degrees through one side of the tubing. More on why in a minute. I fabricated a jig for cutting mine out of a block of wood that was just the size of the tubing. I then cut a notch out of the drilled out hole as a gude for cutting. This held the tubing in place for the cut. Then I just pulled the tubing along the trough and cut some more. It held the tubing firmly in place for the cut.
As you can see, the placement of the hole in the wood is such that the razor blade doesn't cut the bottom of the tubing.
3. Take the tubing, and this is inmportant, and stretch it until the support thread in the tubing breaks. all or most tubing has a support thread in it to keep it from collapsing when bent. Do this all along the lenght of the tubing. Now when the tubing is bent with the cut edge in the center it will not pucker out like this.
Instead it sill look like this.
If you have any other questions, I would be glad to answer them.
Bill