Well, not much really useful info came from this post. Funny how many can tell you something is not right, but can't say what is correct when it comes to variations.

Any way, I have learned a lot talking to a rebuilder and also a parts distributor. These pumps are not hard to rebuild and I do think that almost all of the ones you find on the bay or in junks piles have been rebuilt at one time or another.

As a summary, for the hemi years and about late 68 and up. Hemi and AC cars received the 3.50" 6 blade stamped steel impeller. The pulley ratio was such that hemi cars turned at a 1.2 ratio, and AC cars at a 1.4 ratio. WP turning much faster than motor. Normal cars had a .95 ratio pulley set up. The 8 blade 4.375 impeller is what the normal cars received. You get all this in the service manual.

If you look at the hemi performance documentation from Chrysler, they recommended changing to the smaller impeller. Not for better cooling, but to reduce load on the HP from the WP. Same reason for the thermal fan unit. At higher speeds it reduced load on the motor when the fluid clutch would slip. Yet at idle the higher pulley ratio would push enough fluid for cooling despite the small blade.

Most of the water pumps you will find have an oversized shaft bearing so the hub will stay on after the first rebuild. Crane sell different mechanical seals based on how many times the unit is rebuilt. Sure indicator to tell it has a previous rebuild. Also the OS stamp on the pump casting (Over Sized). Also the 2 piece impeller. The impeller can be pressed on and off a serrated collar that is pressed on the shaft. Made it easier in rebuilding and could save a good impeller.

Here are some pictures of the disassembled pump. Waiting on the new bearing and mechanical seal. You can even get new 6 blade impellers, hubs and the collar device if you need them.