There was no Posi version of the torque tube rear. Positraction became an option on 1/2 tons in '59, using a Spicer 45 axle w/3.92:1 gear. You mention in your first post that when the left wheel was stopped, the right wheel would turn faster. This is normal for an open differential, a Posi differential would not allow you to do this, it would have locked both wheels together.
