The conical washers in your picture are not the correct washers for the two end exhaust manifold studs. Those take the special brass washers that are counter sunk to accept the correct castled type nuts that go in that location. The correct brass washer is on the left in the picture below. The conical washer on the right does NOT go on the end studs on the exhaust manifold. And yes, you must use the correct hardware in the correct location, or else the manifold(s) can crack and break since they expand and contract at different rates. They must be allowed a slight bit of freedom so to speak. The advice to put the conical washers on those locations is incorrect.
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