Weird cooling on my 84 D150

I've taken a few water pumps out of their housings before and found bad impellers. Either loose on the shaft or impellers nearly worn down to nothing. It may not be the most likely cause but I wouldn't rule it out.

I have a 70 and up style alum water pump...I wonder if there is any difference between the 2??(unknown origin on the 70 and up style)