In my 56 Belair I have already installed Eastwood Heat and Sound sound deadening foil-backed material on the floor metal. Then I glued down some foil backed jute carpet padding underlayment. The carpet will go on top of that. My question is do I also need to buy and install the black firewall insulation pad or is what I have sufficient?
If using original size carpet, the original pad has a rubber flap that goes over the carpet to finish it off. If not using it you may have to get carpet that goes up higher. I think that is a special order or custom job. I used polished stainless bolts and hardware to hold my pad in. But to your question it's totally up to you.
Here's what I did on my 55 with the Eastwood silencing foil on the firewall. I put some insulating foil on the upper section. With the firewall pad and silencing foil it was a tight fit for putting the heater distribution duct.
I used a combination of stock and repop fasteners to attach the pad to/through the firewall.