What do you mean your firewall is damaged, is it craked where the clutch cable is? (if its a manual?) If so you can fix this by making up a plate to go over the cable outlet. Changing a firewall would be a massive job. Most simple way would be to cut out the damaged area and replace it with a section from an EB Firewall. The laminated firewall would make it quieter but Ford only do this cos they use thinner & thinner material on every model. Being that you've got a Fairmont I would assume they use a lot of sound deadner anyway.