I have the Weiand water pump on my P-car and works great. No heating problems in 100-degree stop-n-go traffic either. No bypass so it can use a standard 351W thermostat too.http://www.banzairunnerpantera.com/updates_thermostat.htm
Here's the blender style impeller on the Weiand:
And I believe it's the same pump that PIM sells:
Here's the back side of a Flow Kooler - the middle one is similar to the Ford 351C - which has the blender type impeller, barely visible behind the impeller backing plate)
The impeller backing plates can be purchases separately too. I think Quella affixes them to the Weiand water pumps he sells:
The Edelbrock 8844 water pump for a 351C uses a cast impeller:
FWIW, I believe Jack DeRyke has had a Weiand water pump in his Pantera for about 15 years with no trouble at all. And several guys in PCNC who run Flow Koolers and have had no complaints and report that they cost a lot less than Weiand or Edelbrock pumps.