Hi Joel,
You can add GPU water block to this system without upgrading pump.
But you also need to add a radiator too.
And then the flow speed will be low.
It is better to upgrade the pump to BPTA-PHCL.
You can buy it from Newegg too.
https://shop.bitspower.com/index.php?route=product/product&product_id=8190&search=hercu
https://www.newegg.com/p/37B-000X-00537?item=9SIAEMWHE50010