Yo! I think this is the rubber flooring I put in FRANKENTRUCK:
http://www.lmctruck.com/icatalog/cc/full.aspx?Page=110
part number 38-2835. You'd need 38-2836.
It's perfect! When it went in:

It had sufficient extra to trim and fits quite nicely. Covers halfway up firewall to rear edge of shelf behind the seat and to each door threshold without any trouble. Good, heavy, rubber-like compound.
I backed mine with 1/4" foil backed wool,...but not really necessary. It has 1/8" felt backing.
Todd.