Interesting. You and I are apparently of the similar mind when it comes to fabricating things. I'm not rich and I don't buy anything I can make or do myself. I built my own '32 style grille insert very much the same way you did. Check out the pics in my gallery. I also used 1/4 inch round stock for the perimiter and center bar, but then I switched to 1/8 inch rod for the remaining bars and spaced them 3/8 inch apart. After trimming the ends, I added two cross bars behind the verticles to add strength and more closely mimic a real '32 grille. It is held in place with four 1/4-20 studs welded to the back. After painting it, I finished off the look by adding a chrome trim ring around the perimeter. It's made of stick-on chrome moulding (plastic) available at the local parts store. I spliced the ends of the chrome at the top where it's least visible.

I shaped my perimiter piece directly to the shell and it was a difficult wrestling match. I really like your idea of using the plywood form to help shape that piece. Next time I will use your method. Thanks.