I think you'd be surprised how much the junkyard will charge you for a set of headlight assemblies.
They'll charge at least $75 apiece if they're all yellowed, and $100-125 is what you'll pay for one in decent shape.
That price, plus $100 in fiberglass work, and you're talking about $500 for your project.
My question is, if the headlights are flush with the body, and you add a fiberglass cover to them, won't that create a "bulge" in the smooth body lines?