I did it. First with strips of Kilmat then with Dynamat under hood liner. It works no doubt about it. I suppose it would be fine with the underhood liner alone if you were only worried about heat, but the Kilmat strips really made that hood feel solid. When I open my hood after a summer drive, even after its been shut off for several minutes, a gyser of heat rolls up out of there. Its quieter. Driving down the road too. Here's a pic I took halfway thru. It takes two boxes of the underhood liner for full coverage.
Edit: Here's the thread from when I did it
http://67-72chevytrucks.com/vboard/s...d.php?t=808418 I was going for noise reduction but it definitely contains the heat too