I have a set of C8AE-h heads and a 390 block Both the heads and the block have water jackets front and back and all of the head gaskets that I can find only have cut outs for the back set of water jackets way is that.
They are made like that for water travel. From the water pump the water flows trough the block to and up though the head and then trough the intake manifold to the thermostat then into the radiator. You can use your heads on either side of your block.
I just read what I wrote....it doesn't sound very good,... let's try again, Your water is pulled from the radiator into the water pump and flows trough the engine block to the rear of the block, then up through the water jacket at the rear into the head. the water then flows forward to the front of the head and then flows into the intake manifold to the thermostat, and then back to the radiator.
And the reason there are 2 coolant slots on each head is because the same head casting can be used on either the right or left side. With the coolant slots designed to be at the rear for the coolant loop the front slot is simply blocked off by the gasket.