Gene Winfield did his own plexi fab for a few rods he built. He mentioned that if you were to take your form (your old hood)and lay the plexi over the top, place it in an oven where it could soften the plexi. The oven could be as simplee as a box with a few 500w quartz lights to provide the heat source.
Question,
How do you intend to support the plexi. Even with shape, its pretty flexible. It'll grind your paint away wherever the edge touchs. Holding it down with hood pins?
Fiberglass may be your better solution, but you'd better think how to reinforce it. Otherwise, it may end in your windshield when you hit 60 mph.