Fiberglass is wavy because it's not solid like metal. Check out the streetrod market like a 32 roadster for example. Alot of fiberglass bodies out there, but most have steel hoods, hood sides and grill shells.
If you can make a jig and mold to make the hood and then hold it while your bodyworking, sanding, polishing it should be pretty flat and straight. Good luck sounds like a fun project!
