71, 198 slant choke

Without it there'll be a large, loud, smelly, dangerous exhaust leak under the hood—big enough and near enough the engine's air intake to make the engine run poorly under some conditions, and big enough and near enough the car's air intake to make the people inside sick or dead under some conditions. If you can't get this gasket (and you pretty much can't), either make a new one out of appropriate material, or install a different exhaust manifold.