[quick86silver]

Its a flow issue regardless of air or water or a heat transfer issue with the contacting surfaces.

Sounds simple but sitting in the driveway will not allow airflow through the radiator and block.

How many cores is the radiator? 3 Core won't do it even if it is aluminum I have learned.
Are you using a fan shroud with those fans?

What is the flow rate of the water pump? High flow water pumps can sometimes not allow enough contact time in the radiator for the fluid to cool, I have had this problem at high speeds. Running without a thermostat can cause this too.

Has the engine been rebuilt causing a tolerance issue?
Were the water jackets cleaned when the motor was rebuilt, sometimes corrosive buildup can hamper cooling.