I know this gets discussed fairly regularly, but I ran across a page that illustrates a couple of potential differences in water pumps. Water pump pics As you can tell by the link, those are Oldsmobile pumps, but nonetheless, same idea as Chev. Here's a GMB pump with the tack welded plate visible. Notice the impeller blades are further from the housing in that application though. Pretty easy to tell with Olds, since there is no back cover/gasket. I've been thinking based on what I've seen in the above links that it would be beneficial to check your new waterpump design. I have no problem with cooling, but it's pretty obvious the larger impeller alone is going to work better, and would be something to consider for those that want additional cooling capability.