Just got a response from Jerry (Hotrod Lincoln) on the head gasket. His first idea is coolant loss from a cracked or warped head.
Mill the head and check the block with straightedge and feeler gauge.
I want add that the 216 is bad to have build up of sludge, around the rear cylinders, that can be hard to clean out.
This area can overheat and head warping is know to happen. How to clean the block in the truck has been discussed before.
I would first take the head to a shop and have it checked as well as check the block. See what you have to work with first.
