Small block Water Pump

Hi All, This might sound like a Dumb Question,but.. When building a 340 with X Heads, can a 8 blade water pump be used or would it have to be a 6 blade? I have heard that an 8 blade can only be used with Aluminum Heads.Any Comments? Thanks, Craig.
I have a Flow Kooler water pump see this thread: http://www.forabodiesonly.com/mopar/showthread.php?t=67209