Hi, I have a 69 fastback and I have a ton of rust under the cluch pedal in the interior and it looks to be rotted through directly below the clutch pedal. Does anyone know what that part is called and how big of deal it is to replace, it looks like I cant access it from below. Thanks for any advice.

 

Its called the floor pan. And replacing it is pretty involved. Call around to body shops and ask them what they would charge to put one in.
-P.

 

I know in a 67 its called a firewall extension pan. It usually means there are more floor issues than just that one...not to freak you out, not a huge deal.

 

Oh, and I had mine replaced this past spring. rarely just one is bad. Mine led to all floor pans and some rocker issues as well. Have it looked at, but its not uncommon in old Mustangs. Often times the firewall extension pans are gone beacuse of the cowl leaking vs. the obvious undercarriage rust. Not sure if 69s had the infamous cowl issue like the 65-68s do...