Originally Posted by mooneye777
those are the pre 81 valve covers. synthetic should not make any difference. as long as you have a vented radiator filler neck, with a vent tube running to a puke tank, or right to the ground. Then It cant be over filled. And 99.9 percent of radiators made are vented. If it does not have a puke tank you need one. When the car is running (start from cooled down) Squeeze the upper radiator hose that goes to the thermostat housing. If it is tight and firm the thermostat is closed, as soon as it opens the hose will be softened and you will be able to squeeze it flat. check your temperature at that point to verify the themostats operating range. It should open at 190 or so for a carburated motor with the heads you have.
What type fan are you running, from a water pump pulley, or a radiator mounted unit? If its a pump mounted unit does it have a full shroud from the radiator to the fan blades? If not that may be your problem, and an additional radiator mounted fan might become a nessacary item, and cheaper in the long run to get, then modifying a shroud in a custom fit car like yours.
here is a pic of my puke tank set up from the filler neck.