This is definitely one of the most popular subjects that people email me about. Hopefully this will help those of you weekend warriors save a lot of money by not buying that "Speed Grill". Both top and bottom pieces are made similarly, but since the top is slightly more difficult I'll focus on that, in hopes that if you want to try the bottom you'll be smarter. Also worth noting. Make sure to file the edges often! Your hands WILL be bleeding no matter how hard you try, but at least I can say I warned you :)
Pick your mesh! In the wild, the aluminum mesh is better known as "expanded flattened aluminum", and it comes in a billion and four flavors. There are different alloys wich give for different hardnesses, different thicknesses, different size holes. Your absolutely positively best bet is to go to your local welding supply shop and see what they have in stock. From there choose one that looks like it has the right size holes. Make sure it's durable yet bendable enough for you because if it's too stiff then it'll be too hard to work with. Also make sure it's durable enough to not feel like it'll dent just from the wind on the freeway.
Remove the grill! Unscrew the 5 obvious phillips head screws on the top. The front of the grill has 3 small clips(more like buttons). Depress the clips to release them from their mounting points.
Cut your mesh to size. I start off by cutting 1-2 inches around the edge of the grill. Make sure that the mesh is lined up the way you want it, or else the "diamond" pattern may end up being slanted when you're finished! Verrry unsexy like marathon feet.
Bend away! Using your various pliers, teeth, and vise, bend everything that looks like it needs to be bent. I got the best results when starting at the bottom edge. Keep bending and test fitting on your RAVie. You'll find yourself trimming more and more the pieces you bend, but that's totally expected, or else the mesh will really bunch up where it overlaps. Note the top edge in the following picture. I cut out a section so fingers would not be sacrificed when opening the hood... that's where the hood lever is located.
Keep bending until all edges are bent back, and you can close your hood. Make sure that everything looks EXACTLY the way you want. At this point, you can still work with the shape to fill in any gaps or "dents", so it's really worth your while to look at it from all angles.
Mount it dude! Time to get slightly magical. I invented small aluminum flat brackets with holes on each end... maybe 2 inches long and 1/2" wide. One end of each bracket mounts to some of the original 5 grill mounting holes using the original screws. The other end of each bracket mounts to the grill itself with a nut and bolt.
In the front of the grill, I invented 2 "L" brackets that are JB Welded to the backside lip of the bottom of the grill, each lined up with where the tabs are that held in the front grill clips. On the tabs I mounted small spring clips that allow screws to be inserted so that I can mount the "L" brackets to the clips. The result is a grill that is very well supported pretty hard to dent.
if you have any questions. Happy RAV'n!