I first made a wooden mold to match the lower section then I shaped 22 gauge medal around the mold to form the new bottom section. Sounds simple but it took several hours to make the mold and shape the metal. I modified old chisels and bits of scrap metal to help hammer the metal into place. I was surprised at how good the part turned out not having done anything quite like this before.
I had planned to weld the new part on with a mig welder which I have some experience with but don't claim to be a pro. After test welding together several old and new pieces of metal I decided I wasn't experienced enough to do the job with a mig. After doing some research on the web I decided to buy a micro torch. This turned out to worked great so I was able to attach the part and recover the grille.