Jim, don't panic. You'll figure it out.
Let me offer one other suggestion in addition to cleaning out the rear drain and placing a large fan in front of the radiator.
Next time you fill the block with coolant, loosen the temperature sending unit. When coolant weeps from the temperature sending unit, snug it down. The temperature sending unit is at the top of the water jacket. Using it as a bleeder releases any trapped air as you fill the engine.
Good luck,
Matt
