The Power Lock differential bolts together with small windows where you can see the spider gears. The Track lock is a one piece machined casting with big windows that you load the clutches through. I have one of each in my Kirkland garage, the Track Lock is worn-out and the Power Lock is supposedly fresh. The Power Lock is the stronger case of the two, they are both for the 3.54 to 4.10 gears and 30 spline axles. The Ford Dana should have 14 or 16 spline axles, weaker than higher spline count units, but that should be one of the first things you change anyway.