Us a felpro 1255 intake gasket for your vortec heads.
Do not use the factory intake bolts withe the ball on the end with this gasket.
Get your own new stainless bolts from the hardware store. Make sure the length is right
Put at least one steel washer under each manifold bolt. More if require, if the bolt is too long and bottoms out.
The outer 4 vortec manifold bolts need a dab of the black Permatex on the bolt threads.
Let the bead of Black permatex on the china walls of the block set up overnight after installing the intake manifold. Must be clean, dry and oil free for the Permatex to stick to the steel.
Do not over torque the intake bolts.
retighten by hand with a wrench after a few heat cycles.
DO not over torque.