Be sure you get EVERY piece of the old gasket off the head and header before installing the new gaskets. I once replaced gaskets on a big block Chevy, didn't take the header all the way out thinking this was a quick easy job. When I started it up it ticked a little, so I tightened the bolts a little more, and then a little more, but the ticking didn't go away. Pulled the header back off and found a small piece of the old gasket still stuck on there. BUT, since I had continued to tighten the bolts I bent the header flange and wound up buying a new set of headers as a result of my stupidity.
Also, I recommend the Fel Pro composite header gaskets. They are re-useable and last for years. I have a set on my Corvette that was on the first engine when I blew it in 2004, still sealing great on the new engine seven years later. Just put a set on the GTO last year.
'68 GTO, 400/TH400, AC/PS/PB/PW, hideaways, Hurst dual gate
'72 442 'Vert, 350/TH350, AC/PS/PB/PW
'74 Corvette, 383/4-speed, 450 hp, restomod
'71 Javelin, 304/3-speed
'70 Cougar XR7 'Vert, 351W/FMX auto *SOLD*