Success! A gentle pry with a screwdriver was just the ticket! Rocking the alternator back and forth while trying to pull it up had no effect.

Now that I can see the nut on the bottom mount you've talked about (looks kind of like a threaded sleeve), I was thinking I could have sprayed some WD on it and gently tapped the bolt while it was still partially threaded into the nut to push the nut out and create a little slack.

Really appreciate all the help I've received here! Kudos to all!