Flowkooler water pump for 340 going into a 1964 plymouth valiant

Probably. Why would you run a 3 row, when there are THOUSANDS of online articles and forum threads that all agree the two row with two BIG tubes cools the best? Did you just somehow miss that? When you start stacking rows in front of each other, you reduce the cooling efficiency because you start blocking the rows in the back from air flow. It's been proven time and again that two 1" or 1.25" rows of tubes has the best cooling capacity in most cases. Also, Champion is by FAR not the best brand of radiator. Good luck with your decisions.