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When I replaced my cracked manifolds last summer (with another set of manifolds I had around for emergencies) I used gaskets, and haven't had to retighten, and have had no problems with them. I figure that it helped them to seal better, thus perventing leaks. Just my $.02.
I'm putting gaskets on my '74 big block - also did not come with gaskets originally. I trimmed them some so they weren't as obvious to the casual looker.
If you have absolutely flat head exhaust surfaces and absolutely flat exhaust manifold surfaces, just like when the engine was new and the manifold was new, you won't need the gaskets. Otherwise use gaskets.
If you have absolutely flat head exhaust surfaces and absolutely flat exhaust manifold surfaces, just like when the engine was new and the manifold was new, you won't need the gaskets. Otherwise use gaskets.