Follow up...
Wow, it's been a while since this post. It turns out the lower unit is seized. Water leaked in some how, and it sat that way over the winter. I opened the oil drain plugs and mostly water came out.
In my experience so far, it's nearly impossible to get a lower rebuilt economically. No one would give me a flat rate quote. A used, apparently working, but not rebuilt lower goes for about $400.
I bought the exact same motor, used, in excellent condition, used in fresh water only, for $850. So, that's my solution.
However, I'd love to get this one fixed and running. If anyone can help, or knows of an economical rebuilder of lowers, please, please let me know!