I've been away from big blocks for quite a while and my memory is a bit fuzzy. I'm putting together a basically stock '68 HP-383 that will be going in a non-AC '69 Coronet with highway gearing. I have both pumps, a 6-bladed impeller and a 8-bladed one. I know one is for AC and the other non-AC, but I don't remember which is which. All the modern listings don't specify a difference anymore. When I ran this same engine almost 20 years ago, it had the 8-bladed pump and ran just fine in the Florida heat, never getting over about 170degrees even in traffic. So which pump should I go with?

...I think the 8 blade is the A/C pump.

lol, both wrong.
6 vane is the a/c.

the a/c uses a smaller pulley so it spins faster.

8 vane is the non-a/c pump. uses a bigger pulley and spins slower.

They are afraid the 8 vane with the smaller pulley will cause cavatation and cause damage.

use the 8 vane pump & weld on an anticavitation plate on the back side of the vanes between them & the pump whereas on a SB the plate would be welded on the other side facing the timing cover

I thought the 8-blade was the correct one. From the look of it I'd rather use it anyways. It's made by Bosch and it's a beefy affair. The shaft is almost twice the diameter of the 6-blade and the nose is turned down to 1/2" for the fan spacer register. I also understand it's newly manufactured and not a rebuild. It also didn't cost me a dime. The old 8-blade unit was purchased from Pep Boys back around '91 or '92 as part of their lifetime warranty 'True Blue' line. So on a whim I took it down there to see if they'd stand behind it after all these years and they did. A reman wasn't available so they asked if a new-built one was acceptable. Three days later it was here. I'm still going to keep the 6-blade reman as a back-up. A big thumbs up to Pep Boys.

Do your motor a favor and put in a hotter stat. 170 is too cold. Too much cylinder wear with sub 180 temps and youll have better driveability and emmissions including better mileage due to more efficiant combustion.

The 8 blade deal is the correct and hard to find one.
The 6 blade is a universal replacement and came about in the late 70s when most cars came with A/C.
I run the 160 t stat and the engine is a lot happier with today's fuel..., than the warmer ones..