Unless you are planning to race the car just keep the steel. I helped a friend who built a Shelby fast back mustang and raced it a few years back in Drag Week. It was a royal PITA to make to look like it wasn't what it was, and by that I mean wavy fiberglass. Sure some brands may be better but if you have steel I would say spend the money straightening that. If it wasn't a race car I was buying, I would walk away from a car with fiberglass panels.
