Well in the past few minutes, I have done a few searches on Google on two of the proposed mediums in which I could make this sheild out of. And I have a few questions for you guys...
Plexiglass - From what I found, normal Lucite plexiglass has a "maximum service temperature" of °F 185. Now, I'm wondering if the underhood temps would actually reach that high? I might still have some reading to do, just wanted to throw that out there and see if anyone knew off hand.
Aluminum - I was looking at three different grades of aluminum sheeting and found a bunch of info that just throws for a wicked loop! Sorry, I sleep in chemistry class so...

I think it would be much easier for me to actually give a link to the page I was looking at and then point out what caught my eye.
www.technicalmaterials.com. I was looking at the 6th block down on the left, Thermal Cond. What the hell is this talking about. I really want to know, because I don't want to just go out and buy a simple piece of aluminum and find out that it is crap for what I will be using it for. And Pete, I've been thinking a good bit today about the use of rivets to hold the three peices together and I am really likeing it.
The only thing that I can find that I might have problems with making this out of fiberglass is it's ability to take abuse. I mean, we tend to pull our air filters alot and I'm a little worried about how it might hold up to all this. Remember, I am trying to work into the design a way to bolt it down in the rear and at the fender. I'm just a little worried that, even though I will have rubber (or something like that) at each of these bolted points, would the overall structure be able to stand up to the abuse that we tend to put something like this through.
Anyway, just some ponderings I was having. I hope to maybe to do some talking with some people tomorrow, but it may have to wait until next week.
As for the GB idea. Guys, I know that it was first brought up as a joke, but it's really starting to scare the crap out of me. Let's get this first one made. Then we will go from there.