This is one area I have some expertise. My younger brother is the design engineer for Northern. First off I will tell you that my 347 @ 460+ HP was the design mule for the Northern alum rad. It's a two row down flow stock replacement unit. It will cool just fine as long as you have good air flow through the rad. Air flow is more important that the size of the radiator. The later model cross flows are better but the plug and play of the original is a big plus.
The large tubes of a two row alum actual have more surface area exposed to cooling than a 4 row brass. They are much stronger so you can add a higher pressure cap they have no dead areas where the tubes are soldered to the tank bottoms. Just get the summit brand (Northern) but be sure and have a good electric fan or get the universal shroud kit and a good fan. Not one of thoughts small blade flex fans either. It has to be a fan that will pull air through the rad at slow speed. If you do this, it will cool a 500 plus HP motor all day long. If it were me I would get a 17" electric fan and shroud. That will end your problems.