Riviting a fiberglass hood?

Since you have a race weight hood, I'd pin it for sure. You will probably have to get some longer 1/8" rivets in order to go through the plate, the hood, and the washers to keep from cracking the hood itself. When you buy the rivets, check you local hardware store for machine screw washers. IIRC, they will be for 8-32 machine screws, they work to distribute the force of the rivets under the hood. And, I would use aluminum rivets, not steel because the aluminums are much easier to drill out it you happen to make a mistake.