You have the thermostat's block recirc blocked. Are you using the heater hoses to allow coolant to circulate when the thermostat is closed? Might even run without thermostat.
I could see Doug's comments about red hot manifold would also cause one head to be hotter than other.
BTW, how are you determining one head is "steaming"? would that be from your installed head vents? are those vents only at the back of the engine or at the front also
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