I have had the same problem with my 68 505' fastback. I hate header wrap and took it off. Had the headers hi heat black coated, no fiberglass any more !!
I installed some chromed plastic marine vents in each side , (ABOUT 18" X 3") beside the 6 pack scoop to let air out. The one on the pass. side is warping from the engine compartment heat . I do not have cooling problems with the engine it self now tho , I got that worked out last summer. Just the under hood heat. Think I`ll get s/steel vents , if I can find the right size to fit the holes, I`m sure they help cooling the engine too.---------
