Well, I give up. At least for now. I was actually able to twist the post by clamping the saddle in the vise and wrestling with the frame. (I was replacing the saddle in the first place.) But then I took the saddle off -- and found the hammer marks. This post was hammered in, hard. The post is downright mushroomed on top. So this bicycle has only one saddle height. Maybe I'll return to it on a quiet winter day, and play with acid and dry ice. But I have 15 other bikes to tune up now.

Thanks guys! Hopefully I can contribute something on this forum eventually.