408 Stroker Short Block Details: Blueprint Engines

Fiberglass is easy. For an air dam/splitter use some 1/8" steel rod, shape and weld up a bracket so its a bolt on to fit the body.
Then using Flannel shirt martial dipped in Polyester resin, stretch it over the rod bracket. Add some here and there to get the shape where you want it and then lay a layer of fine woven glass cloth over the outsides and some coarse chopped glass on the insides. Basic non 'Ribbed for her....' Condoms filled with moist sand can be shaped for curves and then popped to remove the sand. ;)

If you mess up, grind the bad section out and reglass in new.

Just a down and dirty mod to his picture:
Van.jpeg