Because I didn't know which water pump my car had, I ordered a 6-vane and an 8-vane water pump from A1-Cardone. The photo shows that A1-Cardone puts the 8-vane into both the 6-vane and 8-vane box (notice the 2 different part numbers). Both water pumps were returned. Beware!
Not surprised. The only question is whether that was on purpse to save $$ by reducing inventory or an oops. Cardone 'Select' - that must mean they actually selected the ones that looked OK before boxing 'em.
About 15 years ago, my local parts store picked up a pump for me, when I took it out of the box, the inlet had been machined flat. It must have been for the special hoses that were D shaped instead of round. LOL. We opened the next one on the counter and the impeller had been put on so far, it scrape the casting. Those were both A1 Cardone products and not the only times that I've been unimpressed with their QC. (Not that they are unique in this).
Anyway, to the question about number of blades. The A/C equiped cars generally got impellers with less blades. On the early (driver side inlet) LA engines, diameters were different too. For the '70 up, probably the same. You can check in a shop manual - mine stop at '69.