Car audio guy here....

CRUZE 418 said
I am surprised that only one person has said anything about sound deadening. If only my '69 and '72 Darts were as quiet inside as my '15 Chrysler 200. My modified stock radios are fine for me, but you have to blow your head off with volume to overcome road/engine/exhaust noise. So I am trying/experimenting with sound deadening. I already have quiet flow Walker mufflers in, and will be installing Dynamat in the '72 this winter. Just not sure how far I will have to go with it to achieve a quiet interior so that I can hear the radio.

I put Kilmat in mine a few winters ago. I had the interior out anyway, I ended up buying a box of it big enough to coat everything. I started on the firewall where it met the dash and went all the way to the back window. Overkill for sure, but I wanted it to block heat as well. The difference was night and day, I still have a few squares of it left, I plan on putting a piece inside each door as well this winter.