I found an old school water pump rebuilder near me in Dearborn Heights, has been doing it for 45 years. I was very pleased with the results. I took two C6OE and one C8OE pump and he pulled them apart, then proceeded to point out the different aftermarket components in the two that were previously rebuilt. He knows his stuff, and has parts come in from all over the world.
Tri-parts custom rebuilt water pumps - Dan Bailey (313)530-2893 He does the work in evenings and weekends, so that is probably the best time to call. Eastern time zone.
Note that I'm not involved with this in any way, just sharing what worked for me. Very reasonable pricing.
