I made my own stainless firewall cover out of brushed stainless steel. I didn't want a mirror polished surface in the engine compartment that I'd never be able to keep clean.
I made a cardboard template by taping together a bunch of sheets of printer paper to cover the entire firewall from the engine side, then rubbed the side of a socket against the top edge lip that secures the engine screen and side covers, and also the center opening, which resulted in giving me the perfect trace line to cut, and transfer to cardboard. I then fitted the cardboard a number of times and made minor adjustments and cut the various holes for hoses, etc. before transferring the template to a 2'x4' sheet of flat brushed stainless. I left the stock asbestos insulation on the engine side of the firewall and lined the back side of my new stainless cover with Dynomat, then screwed it to the firewall, sandwiching the original asbestos.
I imagine you could find another suitable (or even more efficient) insulation to replace the stock asbestos. You could always use one of these products for heat insulation, then line your firewall cover with Dynomat for a little more noise insulation.
And here's a less expensive alternative to Dynamat...