posi? trac lock? limited slip? open?

A locker or tight LSD will have both wheels turing the same direction assuming the tranny is in neutral. It is possible that you do in fact have an LSD but if so the clutches are worn out completely.
 
I've smoked both tires with an open unit also... the Mustang is so light its not that hard smoke both a little, especially is the road is a little wet or dirty. Just pull it apart while its sitting on the ground. There is an obvious difference in posi and open differentials. If it checks OK, just seal it it back up with some oil resistant RTV.
 
well, the rear, is, indeed a trac lok. Maybe I was just not paying attention or tired when I was originally turning the drums.

I turm the yoke and both wheels turn fwd. I hand turn one wheel and they both turn fwd :)