I'm finally getting back to building my new engine for my truck.  After tearing down a 312 with a broken web,  I put the heads up on the shelf.  I took them down tonight to clean them up.   When I pulled the head gaskets off,  I found a scratch in 1 head that starts in the  combustion chamber,  and goes all the way to the oil galley in the head.  I can't catch my fingernail on it,  and it was under the head gasket, so it was there when whoever assembled the last engine.   The 312 they came off of was never fired,  and I have paperwork showing they were rebuilt.   Would a Fel-Pro gasket seal this?   If I copper coat it would that give it a better seal?   Or do I need to get this head milled?