Ford 9" Identification Help

just picked up a ford 9" and i don't know how to tell if it is a posi. It came out of a 58 ford car.

 

It would have an "L" on the tag if it still has it. If you look at the carrier where the axle slides in try and spin one side while holding the other, kinda tough to do.

 

As far as I know all non open carriers have the ring gear bolts in a "cove" and opens have a flat flange like yours.

 

This is a non-posi or open carrier and is likely a 28 spline unit.

 

The axels are 28 spline and there is no "L" on the tag so I guess it is not s posi