It would be well worth having the head magnafluxed. You can check the head yourself to get an idea if it is warped with a straight edge. Check the deck of the block as well to ensure it is flat.
The F head is a bit more prone to cracking than the L head. In my opinion, if the water shows up after after running a while, then it would be a cracked head. If the water shows up after sitting overnight, then it would be a head gasket. A cast iron crack will open when heat is applied, while a gasket will deal more after being heated, then cooled back to ambient.
To prevent any rust issues while waiting to get time to year into the head, use WD-40 to fog the cylinder. Then replace the plug.