Some of the gasket sets come with a block off gasket, it has steel on side. I have used them in the past, but they always seemed to be burnt through when I remove them.
18 to 25 gauge (.050" to .0219" ) would work with out altering the manifolds. I have had to use two gaskets to get a old manifold to seal with out problems. You may have to buy a new gasket, then cut in apart to sandwich the stainless steel.
Intake Manifold to Exhaust Manifold Gasket
Part Number: FPG 9763
Product Line: FEL-PRO Gaskets
Part # MS9786 Full set including solid gasket.
Joe