Besides tube size there are other factors such as materials and construction methods used. While brass and copper tranfers heat better than aluminum the solder does not. Aluminum welds tranfers heat much better than solder. Larger tubes have more surface area to dissipate heat. Larger tubes combined with few rows increases airflow through the radiator.
One HP is equal to 42.44 BTUs per minute and is generally 1/3 of the heat the engine produces from burning fuel. Another 1/3 of the heat goes out as hot exhaust, the last 1/3 goes out as waste heat from the radiator. Burning 900 HP worth of fuel will only get you about 300HP.
If you know the amount of fuel your engine will consume, then you can figure out how many BTUs that will produce and compute the expected waste heat through the radiator. Then choose a radiator by its BTU rating. One pound of gasoline produces 19,000 BTUs per minute. One gallon of gasoline weighs 5.92 pounds, so 5.92 x 19,000 = 112,480 BTUs per minute. So GPM X 112,480 ÷ 1/3 should give you a ballpark figure.
Besides the heat capacity of the radiator, you also need to be concerned with coolant flow and airflow. You want a low air pressure zone behind the radiator.