I might be a little conservative here, but I'd leave Grandma's car alone. Fix up and minor shortcomings and just leave it a nice old car. An Impala will never be a drag strip hero, but you'll kill whatever value that the car currently has. There are still a lot of Nova's out there (especially '73-'79 models). Make this nice older car nicer (don't modify it), and then take the proceeds from selling it for a toy. JMHO.