Thought I'd follow up on this. I (1) soaked the sights in Liquid Wrench for about 5 days, (2) put a .380 case on a steel punch as Sakoluvr suggested and (3) got a bigger hammer. Worked great! The rear sights didn't move easily, but they did move.

Thanks everyone.

'Four legs good, two legs baaaad."
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"Jimmy, some of it's magic,
Some of it's tragic,
But I had a good life all the way."
(Jimmy Buffett)

SotG