I have used the stock-type gaskets on several occasions and had no problem w/them- they actually work quite well. You might want to be sure the gaskets don't cover any of the header ports because they won't burn away if they do- they'll stay in the way. Trim as needed. Be sure to retighten the header bolts starting in the middle and working outward. Do this each time you run the engine until they take a set. If the gaskets aren't already cut, remove the bottoms from the bolt holes (see photo) so you can start the header bolts, then drop the gaskets into place- this makes it much easier.