Two days, several hours, lots of aching muscles that I don't use often enough, and the tree stump is down!  24" bar definitely required for this one.

The concrete-embedded pole on the left is what I first tried attaching the winch to.  I hadn't cut through enough of the trunk yet...and it did nothing but lift the massive slab of concrete out of the ground.  Sorry, didn't get a photo of that.

 

In the end, the winch attached to another tree stump did the heavy lifting.  Now, I have to cut it up into firewood!