i had to replace a radiator from howe racing. the radiator spec'd was rated at 400 hp by them from the info i gave them, i'm putting around 550 through it with an
oil/water exchanger. hasn't been a problem yet. i asked if they could make the core tubes bigger and they said too big and it will not flow air, they only offered the one size. current size is either 1" or 1.125". i know griffin will make a larger core radiator cause i have one from them with the larger tubes. i think your radiator would be sufficient imo.
stewart/robert shaw makes good thermostats it seems.