Welding Iron Heads. This drives off moisture and relieves stress. No idea how but cast steel and cast iron is weldable.
Preheating and slow cooling of the component is the crux for the cast iron welding procedure. Larger cracks in cast iron heads can often be repaired by furnace welding or flame spray welding. Of the metal which may cause the welded area to tear and the crack to reopen.
To furnace weld a cast iron head the head is first preheated to 1300 F cherry red in an oven.
If by know the crack is clean ground and drilled the welding preparation can begin. Larger cracks in cast iron heads can often be repaired by furnace welding or flame spray welding. Preheating and slow cooling of the component is the crux for the cast iron welding procedure. If these can be ground and welded along cracks to be repaired i dont see how there isnt a way to fill in a bit of the chamber.