Finally, success. I drilled it out with successively larger size bits until I could get an extractor that I got at Harbor Freight in there and remove it. It was the rustiest bolt I've ever seen in an engine block, and it looked like the pump I removed was original to the car. So that bolt had been immersed in coolant since 1973. I think ten days of soaking it in PB Blaster (and many heat cycles with the torch) finally did the trick. RustyRatRod was correct about the bolt protruding into the water jacket, so when the new bolt goes in it'll be coated with anti-seize. Thanks again for all who weighed in with great suggestions. That's the best thing about this site - guys/gals coming together to share their knowledge. Here's a photo of my new pump that'll go in tomorrow after I paint it. Again, thanks for the many lessons learned!
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