burned 1979 project

As some of you may have read some time back, I am currently trying to fix a 79 vette for a couple that had an electrical fire. The couple couldn't afford to pay for the parts and labor to fix it, so I said I would do the labor free because of my love for these cars. I started diassembling the parts that got torched under the hood, and discovered that part of the fire wall is very soft. It looked fine to the eye, but when I touched it, it just crumbled. Looks like it would be a section about a foot and a half square, but could be more. Won't know until all the bad is removed. The question I have is, will this hurt the structure integritiy of the car? Or can it be fiberglassed over with some success? Some pictures of the car are in my picture section.:huh: