I think you need to give this some more thought. Was there any sound deadener on the floors of 37 coupes? Are you confusing the deadener on the wirewall, doors, quarter panels, roof, with what you think should be on floors? Different materials were used on firewalls.
Firewall Insulation Pads I don't see any R value or sound deadener value in bonding less than ten layers of tar paper together. Have you checked out any materials used on putting a roof membrane on a flat roof?
Sound Deadening Materials Are you interested in some kind of a look or is it hot in North Carolina and you need something to make it more comfortable to drive your car? Here are some product ideas. Have you done a SEARCH of our past posts on this topic?
Eastwood Sound Deadener Products Good luck, Mike