When the head gaskets are installed correctly, the water coolant flow travels through both sides of the block to the rear and then up into the heads where it travels forward before exiting at the intake manifold and then the thermostat.  There are three scenarios for head gasket installation on the Y.  Both gaskets installed correctly, only one gasket installed correctly, or both gaskets installed incorrectly.
 
If the head gasket(s) are installed backwards, then the large coolant hole at the end of the head gasket is at the front of the engine rather than at the rear.  This essentially has the majority of the coolant flow from the water pump going into the cylinder head at the front of the engine and then directly back into the intake manifold to the thermostat.  With the head gasket installed backwards, there’s minimal circulation taking place within the block or the heads which in turn becomes an overheating issue. 
 
Here’s a picture of a correctly installed head gasket.  The arrow points to the coolant hole in the gasket that is the primary path for coolant from the block to the head.  Disregard where the fire ring has been pushed up into the oil galley section.  That was simply the result of low octane fuel and a compression ratio that was much too high for that particular fuel.

Lorena, Texas (South of Waco)

Reading this forum I discover my gaskets are installed wrong. Both square corners are facing the firewall in the upward position. My question is "did ford ever install them like this? Explain again why it causes overheating besides the obvious. Also I have a frozen spark plug which a short while ago was easy to remove twice. Now all of a sudden its frozen. Any tips on how to remove it? How far does it extend into the open cylinder beyond the threads? As always, thanks for your expertise. Charlie