Freewheel disassembly problem
This is the OP, George_San_Jose.  I finally got it turning. I'm not exactly sure what the  critical step was b/c I tried a combination of ideas.  The solution was some  combination of a couple days soaking in thread penetrant, working the job w/the freewheel on the wheel,  and using a steel center punch (rather than a screwdriver) to whack the hole tangentially with a hammer. I expect the latter was the most important, as some of the impact-value from the hammer was getting lost in the plastic handle of the screwdriver.