Well, that seems to have worked. That first pic above is how it came in the pot.
Here's a few more.
This is the solid chunk of clay it came in. I've done natural clay plaster work before, and I can tell you it's very difficult to make a clay plaster this hard on purpose. Wherever this tree came from, I'd love to use the clay there for more than a few plaster projects I have in mind.
Here it is post partial repotting. The red stick in front of it is 18 inches for scale.
My photography skills are not up to showing off what I like about this tree. Nor am I sure I could quantify why it appeals to me. My Dad loved it too. The trunk appears to be well suited to either be fairly upright or more slanted, depending on what we do with it when we fully repot it in a few years (currently I imagine keeping it slanted). That's far enough away that I'm not worried about making the decision of what to do with it.
A week and a half later it seems to still be happy. Though I know it can take a few months for poor health to show. So I'll have a better idea at the end of summer. Right now it's sitting in the shade where it gets a fair amount of light sun filtered through some trees.
Thanks again for everyone's advice. I think I exposed just enough roots for it to get water and breathe, and got a much more breathable soil around it. It's taken a pounding, but much less so than if you all hadn't given me some good warnings. If nothing else, it was quite a learning experience and I'll do much better with future trees.