Well, the JJ is back in my hands. The owner was in his late '50s or early '60s and said he was going through a divorce. He's sold tons of old Mopar parts on eBay as well as a number of guitars and guitar related items. The only question I asked about the history of the bass was "it's an unusual bass to find around here, how did you come across it?"
He said he trades back and forth with a dealer he knows who frequently comes up with guitars he would buy if they were interesting. Now he's having to sell off a bunch of things.
After talking to him in person for about 45 minutes I really don't think he has any idea it was stolen. I felt he was trustworthy and honest and nothing he said was shady in the least. The JJ came in a TKL case and had a guitar strap inside, so at least I got a case for it!
The bass itself is still in great shape with only one or two more scratches or dings on it when I owned it before. There's residue on the back of the neck where tape had been placed, I don't know why.