Exhaust manifolds were installed without flange gaskets at the factory. Typically, I don't use gaskets when servicing exhaust manifolds. I check the sealing surfaces for flatness and alignment, and smear a thin even coat of Ultra Copper on the flange faces during assembly. If the manifolds are badly warped, gaskets won't really help.
When removing an old manifold that you intend to reuse, it is good practice to install "spreaders" before loosening the bolts - two per manifold.
The 'spreaders' help maintain the flange spacing and greatly ease reassembly. Otherwise the cast manifold can distort, making its reuse a frustrating proposition. Once the manifolds move, the spreaders are virtually useless. They won't restore flange position or alignment.
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