Limited slip, posi and spool, how to tell which?

[Jeff H]

The rear is a 12 bolt but not original to the car. It's coded as a 3.07 open but the rear is definitely locked together like a posi or locker. There is no give when you turn one wheel the other goes with it. I thought maybe a previous owner took the original 3.55 posi out of the original rear and put it in this housing. I guess I would need to remove the cover to really see what's going on in there.