Radiator Size ????

IMHO.

get a HP / AC cooling OEM style copper brass new or used OEM radiator.

BUT...

Your fan, pulleys, water pump all have to match the level of cooling you need.

Contact US radiator and talk to them.

Stay away from electric fans and shrouds that are close to the back of the rad and parallel to the rad cores.

remember the factory cooled 340s 383s and even 440s in A bodies without any fancy equipment.