I've had decent luck with Percy's ultra seal header gaskets on 2 big blocks and a small block. Not sure if they are the same as the Napa Ultra seals or not. These gaskets are made of several layers of a soft aluminum material and, according to the package, reusable, but I've never had the headers back off on any of my trucks. They're around $25 a set, but worth it in my opinion. I've also used the paper ones that come with most headers but coated them with permatex ultra copper on both sides like previously suggested.