318 LA rebuild after losing a valve seat

Here us a "Huge To Do" for you. Get yourself a tube of the Very High Temp Silicone Gasket maker, red or bronze in color. Use this high temp sealer to seal the 4 studs that go into the outside exhaust manifold threads in the heads, these holes go directly into the water jacket and need to be thread sealed.

Studs are 5/16 course that screw into head, and 5/16 fine thread that stick out for the manifold to bolt on. The rest of the exhaust manifold bolts are bolts.

Also instead of that cork gasket on the intake, people put a good bead of the black rtv gasket maker there and it will make its own gasket and seal good. Let it set for 2 hours after you torque it down, then come back with a razor knife and cut off the excess that is hanging out if you want to clean it up some.