I'm too late to provide info for Bill, but I recommend for future builders to use #8-3/4" long stainless-steel sheet-metal screws with #2 Philips drive truss-heads threaded into the fiberglass body. Use truss-head rather than pan-head or oval-head screws. The truss-head has a larger diameter, which provides additional bearing surface on the plastic. What Ron says about nutserts is good. You'll then have to go to machine screws when using them. As for Shelby events, I noticed that an original GT40 ran the SAAC 31 at VIR without side glass required or not. Safety is one reason, but ventilation in another, particularly when running without air-conditioning.
Grainger has made it a whole lot easier for builders. They now have about every fastener you'll ever need. Beats going to your local hardware, Lowes or Home Depot just to find out they don't have quite what you need. Plus, the cost for a box of 100 screws is about 50% more than a package of 10 from a retail outlet.