It doesn't fix leaking BTW. But if you have it off, do this. I agree it's the #1 best thing that can be done to improve efficiency of the cooling system.
Keep in mind the link above is showing 1969 setup. Those with 67/68 8-bolt pumps will find things a little different in there...but same concept applies as they have similar divider plate.
Those with 69's and 11 bolt setups should replace water pump sleeves while you're in there too. Often skipped and many re-use the sleeves, and this is a mistake as they also impact cooling flow efficiency after the rubber ends harden and start to degrade with age. They are still available new from GM, as for part #9796347 for a pair. Roughly $20 and always on Ebay too.
67/68 8-bolt setups don't have these sleeves, so don't worry about them.
For both setups cast impeller pumps are far superior to stamped impeller pumps. NAPA sells inexpensive high quality cast impeller pumps made by Gates: TFW 43122 for 8 bolt (67/68) about $72 TFW 43102 for 11 bolt (69) about $38
2 gaskets included, brand new lifetime warranty...not remans. Over-the-counter at any NAPA in the country. No need to spend silly money on "high flow" aftermarket performance brands, or pay 200% markup to repro houses, etc.
Obviously this is all V8. I know nothing about the OHC's.
