That seems a bit large for your setup especially. Shouldn't take much if anything more than a std BBC setup at those power levels. But ya can never go to big I guess.
Dave's only running a 5" by like 26" at 700-800hp. I've never seen his hit 180F in the data logs yet. I'm still considering somewhere around a 6" x 24" double pass that will fit along side the engines.
I would go take a peak at what the local Cummins gurus use on their 700hp. Bet it's smaller than your thinking.
Nice reservoir tanks, like the diamond plate caps. Grinder fix those welds right up..