I *think* they're from a late 80's Cutlass Calais. They're pretty narrow, so it kinda makes me want to build a custom console for it. Of course I had to drill new holes for mounting them and use some old chassis hardware to fasten them down, but overall, I'm really happy with them. They sit well, and they were only like $100.
I also thought about buying some retractable harnesses for it. Don't get me wrong, the shoulder harnesses attached to the roof kinda have a certain charm, but I'd really like something that allows more flexibility.