It's running hot at lower speeds (as is steam, not just high on the gauge). I'll be adding a shroud and a 5-blade viscous fan to replace the mickey mouse flex fan that's on it now, along with new cap, thermostat, cooler plugs, checking the advance, etc. It already has an overflow tank and runs cool enough at speed so I'm assuming it's not blocked up otherwise.

I came across this thread: http://www.dodgecharger.com/forum/index.php?PHPSESSID=qdp6mreo87eglkba11hdrim0o0&topic=60599.0
There's a lot to read there but starting on page 8 there is a comparison of water pumps. Pump #1 is a motor home piece with an 8 blade impeller measuring 4.375" across that has really good flow numbers at low speed. So not only is there a difference in the number of fins, but also the diameter of the impeller, and I'm assuming the pitch of the fins determines the curve of the flow.

It looks like I am better off with an 8-blade pump so long as the impeller is big enough. NAPA makes a stock looking one. I can always speed it up with the smaller pulley I guess, which will give more flow at lower rpms. This is just a street car, it may see a bigger cam as the motor feels pretty tame right now but nothing wild. It's going to see a lot of low speed city driving under 40mph so it'll have to run a little cooler to be happy. The last owner also opened up the hood scoops which doesn't do much on the Barracuda hoods (may actually hurt) so they'll get plugged back up, too.