The restriction would be confined to a very, very small area worst case scenario.
What makes it need to be 8AN? That's 1/2" hose, a seriously fat hose. Is it that the cooler has 8AN connections? Because if all you need is 3/8" hose (6AN) then just run 6AN to the cooler and put in 8AN to 6AN adapters in the cooler. (Like you do for fuel filters with the ungodly 10AN inlets)